LITERATURE STUDY
Status of environmental management in Vientiane
The Lao People’s Democratic Republic (Lao PDR) is near to Myanmar,
Cambodia, the People's Republic of China, Thailand, and Vietnam surround Laos, which has a total land area of 236,800 square kilometers characterized by its mountainous terrain The capital city, Vientiane, is situated on a plain, while the Mekong River borders the country to the west, serving as a crucial route for transportation, communication, and trade with neighboring nations that share its tributaries.
Set in the heart of Vientiane, Laos from the north latitude 17 45'50 - 22'38 18 09'37 5'40 and 102 - 103 east longitude and the natural area 3.920 km 2 Vientiane is the 9 District: Chanthabuly, Sikottabong, Xaysettha, Sisattanak, Naxaythong, Saythany,
Hatsaiphong and Saengthong Phakngum exhibit varying levels of economic development and population density within Vientiane, which comprises 500 villages Notably, urban areas constitute 76% of these villages, while rural areas make up only 24% Vientiane is characterized by a high cultural level, a strong work ethic, and a deep-rooted patriotic tradition, reflecting the community's unwavering commitment to progress and revolution.
Figure 1 Map of Lao PDR
Lao PDR is endowed with abundant natural resources, particularly water, which is crucial for meeting the basic needs of its population, fostering socio-economic development, and supporting ecological systems However, sustainable management and protection of these water resources are imperative, as some provinces, especially remote areas, face water scarcity for drinking and irrigation The growing population has increased the demand for clean water, leading to the exploitation of marginal and polluted sources Major surface water resources include rivers and streams, supplemented by gravity-fed systems and protected spring water, while groundwater is accessed through boreholes with hand pumps and protected dug wells Additionally, rainwater is harvested in reservoirs, tanks, and individual collection jars.
Vientiane experiences relatively minor environmental issues compared to other regional cities, attributed to its smaller size, lower population density, and limited industrial activity.
Despite recent investments, there are still limited systems to guarantee that all individuals, especially the underprivileged, can benefit from environmental enhancements and that future environmental issues can be effectively managed.
The Water Quality Laboratory of the Ministry of Agriculture and Forestry has reported that water quality in Lao PDR has generally been good over the past 15 years However, significant water pollution issues persist in major urban areas, primarily due to the water usage by households, hotels, hospitals, and entertainment centers Additionally, activities in the agricultural and industrial sectors, such as mineral exploitation and hydropower generation, contribute to water pollution Ongoing degradation of water bodies and catchments, driven by sedimentation, land erosion, and drying out, remains a concern.
Poverty in Lao PDR significantly contributes to inadequate access to clean water and sanitation, leading to a high prevalence of diarrhea and dysentery The rising urban and upland populations exacerbate water pollution, while the poorest districts utilize less than half the national average of daily water due to limited access for personal and irrigation needs This situation highlights the urgent need for a systematic approach to water quality monitoring and management Currently, various ministries operate independently in managing water resources, but the Water Resources and Environment Administration (WREA) must take a more active leadership role Enhanced water quality policies and strategies are essential to address the rapid development of water resources and mitigate their impacts on water quality and ecosystems.
The revision of the National Water Resources Policy and Strategy, along with a potential update of the Law on Water and Water Resources, presents a crucial opportunity for enhancing water management practices It is essential to establish coordinated standards and procedures for water quality monitoring Additionally, building capacity and implementing systematic coordination among agencies responsible for comprehensive water quality monitoring and management is vital for effective governance.
In Vientiane, environmental measures for solid waste management encompass both market and non-market instruments, alongside public education and training programs aimed at promoting moral suasion However, rapid demographic growth, socio-economic development, and urbanization are leading to a decline in water quality Urban pollutants, including litter, dust, oil, grease, and debris from vehicles, are frequently washed into drains and watercourses Additionally, residential areas and open spaces contribute sediments and nutrients, while urban drains often serve as secondary sewers, carrying industrial discharges and septic tank seepage, especially during wet weather The disposal of sewage into surface drains exacerbates the contamination of wastewater with faecal matter from latrines and septic systems.
In 2002, wastewater monitoring in Vientiane involved collecting samples from 15 stations to assess parameters such as pH, conductivity, alkalinity, BOD5, COD, and temperature The findings indicated that the average levels of all measured parameters fell within acceptable limits; however, some samples did exceed the standards for Class A wastewater discharge set by the Government in 1994.
Table 1 Wastewater Quality in Vientiane Capital Jan-Dec 2000 [2]
Parameters Unit Range of Avg Results Standard pH 6.38-8.44 7.34 6 – 9.5
Lao PDR has taken significant step to ensure that the country’s environment and natural resources, particularly the forests and use are sustainable management Since
Since 1993, Laos has established an institutional and legal framework encompassing environmental, land, forestry, and water resources laws Despite these measures, the rapid growth of industries, particularly in pulp and paper, timber, food processing, and garment manufacturing, has heightened pollution risks Many of these larger industries have inadequate wastewater treatment systems, contributing to environmental degradation, while the proliferation of smaller industries further exacerbates the issue From 1999 to 2003, the industrial sector's contribution to GDP rose from 8% to 11.3%, and the total number of industries increased nearly four-fold during this period In line with the Millennium Development Goals, the government aims to enhance local access to safe drinking water by 2015.
Table 2 Industrial Growth in Lao PDR [2]
For this reason, the government set targets in the Socio-Economic Development Strategy up to the year 2020 for the five years plans For the National Growth and
The Poverty Eradication Strategy, National Environment Strategy for 2020, and the 2006–2010 Action Plan emphasize the critical need for sustainable management and utilization of natural resources, particularly water.
The Environmental Protection Law (EPL), along with the Water and Water Resources Law, strictly prohibits water pollution and holds the private sector accountable for environmental damage and its associated social and economic impacts stemming from industrial activities, particularly concerning wastewater and air emissions.
The government's growing emphasis on the private sector, especially small and medium-sized enterprises (SMEs), is praiseworthy However, it is crucial to place greater importance on export orientation and shift away from import substitution policies, which many countries have moved past after facing significant challenges.
Finally, in according by the presentment of the Minister of Industry and
Commerce, in 2005 has regulation issued of the main condition on the industrial factories
To protect public water bodies and ensure ecological health, it is essential to prohibit any direct or indirect discharge that could harm the environment or human health Factories must obtain approval for their wastewater treatment systems from the Director of the Industry Department prior to construction and submit a comprehensive waste management plan Additionally, the installation of wastewater treatment systems, volume measurement equipment, and necessary monitoring facilities is mandatory Regular monitoring and analysis of wastewater must be conducted, with results reported to the Director of the Industry Department Furthermore, daily records of chemical substance usage must be maintained, including explanations for their application.
1.1.3 Situation of pulp and paper mill in Vientiane
The pulp and paper mill wastewater treatment technologies
1.2.1 Pulp and paper mill production
The characteristics of wastewater produced by the pulp and paper industry are influenced by several factors, including the specific processes employed, the types of wood materials used, the technology applied, management practices, internal effluent recirculation for recovery, and the volume of water utilized in each process.
The wastewater from hardwood kraft mills contains chlorinated phenols and acids at levels three to eight times lower than those found in softwood kraft mills Throughout the pulping and papermaking process, various stages contribute to the generation of pollutants, highlighting the significant pollution load associated with these individual processes.
1 Mechanical forces in the presence of water (mechanical pulping) The process involves passing a block of wood, usually debarked, through a rotating grindstone where the fires are stripped of and suspended in water.
2 Chemical pulping which utilizes significantly large amounts of chemicals to break down the wood in the presence of heat and pressure The spent liquor is then either recycled or disposed of by burning for heat recovery.
3 A combination of the two (chemical thermo-mechanical pulping) The wood is first partially softened by chemicals and the remainder of the pulping proceeds with
Mechanical pulping Chemical pulping Chemo-mechanical pulping (CMP)
Papermaking Thermo-mechanical pulping (TMP)
Figure 3 Process description for pulp and paper mill factory [10]
1.2.2 Sources of pollution in the production of pulp and paper mil mechanical force According by G Thompson, J Swain, M Kay, C.F Forster [10] in conventional mechanical pulping, the dissolved organic material from the wood is split between the pulp passing onto the paper machine and that going to waste The preponderance of the pollutants which go forward to the paper machine will subsequently exist released in the paper machine wastewater, except where the process is operated in a closed loop system In difference, chemical pulping plants, with recovery systems in place, find that most of the organic pollutants dissolved during pulping are retained in the recovered liquors which are generally incinerated The highest wastewater losses are found in mills which operate chemi-mechanical process However, the wood pulping and production of the paper products generate a considerable amount of pollutants characterized by biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), toxicity, and color when untreated or poorly treated effluents are discharged to receiving water Pulp and paper mills generate varieties of pollutants depending upon the type of the pulping process This is made from cellulose fibers, carbohydrates as sugar and lignin, and is adhesive substance for the cellulose fibers The current environmental limitations have caused the decrease of the consumption of the natural resources for this industrial use So, in this industry the recycling of fibrous raw materials and/or alternative is the high water usage, between 20,000 and 60,000 gallons/t of products, results in large amounts of wastewater generation [11, [12] For the water utilization dependents on the technology and the product obtained were 3-8 m 3 /t Carton of product, 10-15 m 3 /t Newspaper of product, 15-20 m 3 /t Paper tissue of product, and Writing paper 10- 20 m 3 /t of product [13] The wastewater from the papermaking and de- inking process differs from the pulping process due to there being no breakdown of raw material, other than the discards of cleaning and screening Foremost sources of pollutant releases in pulp and paper manufacture in figure 3 Process description for pulp and paper mill factory it show below:
The pulp and paper industry relies heavily on natural resources such as wood and water, as well as fossil fuels and electricity, contributing significantly to pollution in air, water, and land This pollution adversely impacts environmental quality, affecting both human health and ecosystems Additionally, the recovery and reuse of water in this industry can lead to higher concentrations of organic and inorganic substances, which may disrupt paper formation, increase bacterial loads, and cause corrosion and unpleasant odors.
According to D Pokhrel and T Viraraghavan, the wood pulping and paper production processes generate substantial pollutants, including biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), toxicity, and color, which are released into receiving waters as untreated effluents.
The study analyzed the concentration of total wood extractives in the influent and effluent of an activated sludge plant, revealing that 88% of these extractives were effectively removed during the process Standard procedures for determining wood extractives involve centrifugation to eliminate larger particles, ensuring reproducible results for dissolved and colloidal substances The wastewater from an integrated Kraft pulp and paper mill was characterized before and after the activated sludge process using micro-filtration and ultra-filtration to separate different size fractions The analysis showed that in the influent, 44% of resin and fatty acids (12.8 mg/L) were present in particles, 20% as colloids (0.45 mm–3 kDa), and 36% in the fraction, while sterols (1.5 mg/L) were distributed as 5%, 46%, and 49% across the respective categories.
In the effluent, resin and fatty acids (1.45 mg/L) and sterols (0.26 mg/L), as well as a small proportion in particles b-sitosterol was present in particles in the effluent (88 _ 50 mg/L) [14].
The used effluents were sourced from the largest pulp and paper mill, which produces approximately 140 tons per day of pulp from both soft and hard woods The mill employs a six-stage bleaching process, including chlorination, extraction, hypochlorite, and chlorine dioxide treatments The combined effluents from the initial bleaching stages account for 30% and 60% of the total pulp mill effluent flow rate, respectively Ozonation experiments utilized spent effluents from these individual bleaching stages, with pretreated effluents mixed in a 1:1:1.39 ratio with other streams from the mill Algal treatment was applied to both raw and pre-treated combined effluents Despite a reduction in chlorinated compounds, concerns regarding the environmental impacts of elemental-chlorine-free (ECF) and total-chlorine-free (TCF) bleached pulp mill effluents persist, with chronic effects on aquatic organisms still being reported The wastewater characteristics generated from various pulp and paper processes are influenced by factors such as the type of wood used, process technology, management practices, and water usage.
Pollution from the pulp and paper industry can be minimized by various internal process changes and management measures such as the Best Available Technology (BAT).
Effective wastewater treatment is essential, necessitating a combination of mechanical, physical, chemical, and biological methods to achieve cost efficiency Understanding wastewater composition involves analyzing total solids (TS), total suspended solids (TSS), and volatile suspended solids (VSS), with a key distinction between dissolved substances and particulate matter Specific analytical methods, such as determining ammonium nitrogen, phosphate, and nitrate nitrogen, are crucial for assessing inorganic and organic compounds Total organic carbon (TOC) and dissolved organic carbon (DOC) are used to measure organic compounds, while chemical oxygen demand (COD) and biological oxygen demand (BOD) are vital for evaluating pollutant levels COD is the primary method for characterizing wastewater, although TOC can be correlated to it BOD provides an estimate of degradable matter, and VSS is the most accurate measure of microbial biomass, while TSS may lead to overestimation due to inorganic matter interference.
Wood preparation involves the removal of soils, dirt, and bark from the wood, along with the separation of chips from the bark Water is utilized to thoroughly clean the wood, resulting in wastewater that contains suspended solids, biochemical oxygen demand (BOD), dirt, grit, and fibers.
Figure 4 Pollutants from various sources of pulping and papermaking [11]
Some methods commonly using to treat with the wastewater
Physicochemical treatment processes effectively eliminate suspended solids, colloidal particles, floating materials, colors, and toxic substances This is achieved through various techniques, including sedimentation, flotation, screening, adsorption, coagulation, oxidation, ozonation, electrolysis, reverse osmosis, ultrafiltration, and nanofiltration technologies.
Chemical coagulation followed by sedimentation is an effective method for treating wastewater with high suspended solids, particularly those containing colloidal materials Research indicates that this process significantly reduces pollution loads and facilitates adequate water recovery While coagulation and flocculation are primarily utilized in the tertiary treatment of pulp and paper mill wastewater, they are less common in primary treatment stages A comparative study evaluated the effectiveness of horseradish peroxide (chitosan) against other coagulants, including aluminum sulfate (Al2(SO4)3), hexamethylene diamine epichlorohydrin polycondensate (HE), and polyethyleneimine (PEI), in removing adsorbable organic halides (AOX), total organic carbon (TOC), and color Coagulation is primarily achieved through inorganic metal salts like aluminum and ferric sulfates and chlorides, while various polyelectrolytes, such as polyacrylamides, chitosan, and polysaccharides, serve as coagulant aids to enhance floc formation and improve sedimentation rates.
A study on the treatment of pulp and paper mill wastewater utilized alum and polyaluminum chloride (PACl), both individually and in combination with cationic polyacrylamide (C-PAM) and anionic polyacrylamide (A-PAM) Key evaluation parameters included turbidity reduction, chemical oxygen demand (COD), total suspended solids (TSS) removal, sludge volume index (SVI), and settling time The coagulation-flocculation process showed that coagulant dosage and pH significantly influence efficiency At an optimal alum dosage of 1000 mg/L and a pH of 6.0, turbidity was reduced by 99.8%, TSS removal reached 99.4%, and COD reduction was 91% For PACl, the optimum dosage was 500 mg/L at the same pH, achieving 99.9% turbidity reduction, 99.5% TSS removal, and 91.3% COD reduction The study also highlighted the effectiveness of combining inorganic coagulants with flocculants, specifically using alum and PACl alongside C-PAM.
(Organopol 5415) and A-PAM (Chemfloc 430A) Overall, alum coupled with Organopol
5415 is the best system among all systems studied It gives 99.7% reduction of turbidity, 99.5% removal of TSS and 95.6% reduction of COD, and at the same time with low SVI
(38 mL/g) and low settling time.
Angela Claudia Rodrigues et al developed a combined method that enhances wastewater treatment efficiency for pulp and paper mill factories, integrating coagulation with photocatalysis The process begins with coagulation-flocculation, utilizing FeCl3 as the primary coagulating agent and chitosan as an auxiliary Following this, the resulting aqueous phase undergoes treatment with a UV/TiO2/H2O2 system, powered by mercury lamps The optimized coagulation conditions were established at a pH of 6.0 and a concentration of 80 mg L−1.
The study focused on optimizing photocatalysis conditions using FeCl3·6H2O and chitosan, achieving effective results at pH 3.0 with 0.50 g L−1 of TiO2 and 10 mmol L−1 of H2O2 Initial COD values of 1303 mg L−1 for the untreated sample decreased to 545 mg L−1 without chitosan and 516 mg L−1 with chitosan Turbidity significantly reduced from 10 FTU to 2.5 FTU without chitosan and to 1.1 FTU with chitosan Coagulation also led to decreased concentrations of N-ammoniac, N-organic, nitrate, nitrite, phosphate, and sulfate ions Absorbance reductions were noted at 500 nm (90%) and in the aliphatic and aromatic regions (70–80% at 254, 280, and 310 nm) While chitosan was not highly efficient for quantitative purposes, it enhanced sedimentation COD values for photolyzed samples showed reductions to 344 mg L−1 for UV/H2O2, 326 mg L−1 for UV/TiO2, and 246 mg L−1 for UV/TiO2/H2O2, with a significant absorbance intensity reduction of approximately 98% for chromophores Overall, the combined wastewater treatment under optimized conditions yielded promising results.
Adsorption is the incorporation of a substance in one state into another of a different state (e.g liquids being absorbed by a solid or gases being absorbed by a liquid).
Adsorption is the process of ions and molecules adhering to the surface of another phase, making it an effective tertiary treatment for removing organic compounds from wastewater, particularly at low concentrations Activated carbon is the most widely used adsorbent; however, its high activation and regeneration costs, along with disposal issues, have prompted research into more affordable alternatives Various low-cost adsorbents, such as wood, coir pith, coal fly ash, bagasse fly ash, and coal-fired boiler bottom ash, have been explored for wastewater treatment Studies have shown that activated charcoal, fuller’s earth, and coal ash can effectively remove color, while activated coke has been utilized to reduce color, COD, DOC, and AOX in bleached wastewater Additionally, investigations into lignin removal have focused on achieving acceptable levels of color and chloride for reuse.
The adsorption process was conducted at ambient temperature using an orbital shaker incubator, where 50 ml of wastewater was placed in five conical flasks, each containing varying amounts of activated carbon After optimizing the adsorbent dose, the pH of the wastewater was adjusted with either 1M NaOH or 1.8M H2SO4 The flasks were shaken at 120 rpm for one hour, after which the treated samples were filtered through filter paper, and the filtrate was analyzed for parameters such as pH, Chemical Oxygen Demand (COD), and Total Organic Carbon (TOC).
Chemical oxidation methods, including peroxide, ozone, and permanganate, have been widely used for wastewater treatment Advanced oxidation processes (AOPs), such as ultrasonic irradiation combined with Fenton-like oxidation (Fe3+/H2O2) and photo-Fenton degradation (Fe2+/H2O2/UV), have also been explored Research has shown that operating parameters like pH and oxidant dosage significantly impact the removal of organic compounds, particularly in terms of COD reduction Studies on Kraft pulp bleaching wastewater revealed that horseradish peroxide can achieve a 50% decolorization of Kraft effluent within three hours Additionally, advanced oxidation systems, including photocatalysis with O2/ZnO/UV and O2/TiO2/UV, as well as ozone treatment, have been effective in degrading phenolic and polyphenolic compounds found in bleaching effluents.
The study found that O2/ZnO/UV and O2/TiO2/UV systems were the most effective for rapidly oxidizing effluents Additionally, the combination of Fenton and photo-Fenton reactions demonstrated significant efficacy in treating bleaching Kraft mill effluent Ozonation, which involves infusing water with ozone, is widely used not only for eliminating bacteria and microorganisms but also for controlling color, taste, and odor.
All ozonation experiments were carried out at room temperature (23-30 0 C) in a semi- continuous glass reactor (230 mL) with the initial ozone concentration of 30 mg/L during
The ozone/oxygen mixture was distributed through a porous ceramic at a flow rate of 0.5 mL/min for 60 minutes in the lower section of the reactor Ozonation of the diluted and filtered samples, following precipitation, was conducted at initial pH levels of 1, 3, 8, and 12.
D Pokhrel, T Viraraghavan [9] have give overall reviews of application of the ozonation processes for the removal of COD, TOC, and toxicity from pulp mill effluent and increased biodegradability of the effluent were achieved after treatment with ozone Their summarized that a 90% removal of ethylenediaminetetraacetic acid (EDTA) and a 65% removal of COD by ozone treatment of the pulp mill effluent after 60 min of ozo nation total organic carbon, total phenols reduced to 12% and 70% respectively, and effluent colors to 35% of bleached pulp mill effluent Several authors reported on toxic compounds, COD, and color removal by ozone treatment Some authors indicated that a high dosage of ozone (100–300 mg/ dm 3 ) was required to remove 50% of lippphilic wood extractives The ozone doses of 0.2 mgO3/initial mg COD can eliminate over 90% resin acid High removals of TOC, COD, AOX, and color from bleached kraft mill effluent (BKME1) using heterogeneous photocatalysis and ozone treatment can be achieved by ozonation and adsorption.
This study explores various treatment techniques for Kraft pulp mill effluent, including ozonation, chemical coagulation-flocculation, activated carbon adsorption, and membrane filtration The combination of these methods enhances the removal of diverse compounds present in the effluent Membrane filtration, specifically, was tested using 10% strong effluent samples diluted in distilled water, with pH levels adjusted to 4, 7, and 10 The samples were contained in cellulose membrane sacks, immersed in distilled water for 24 hours before analysis Ozonation samples were collected from the water that had interacted with the effluent molecules Membrane filtration operates as a pressure-driven separation process, effectively rejecting particulate matter larger than 1 mm, and its efficiency can be validated through direct integrity tests Characterization of the membrane surfaces was conducted using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM), providing insights into the structural differences between clean and fouled membranes.
According by E.Dialynas, E.Diamadopoulos [24] has reported high removals were also observed for various heavy metals The removal values were above 90% for
Ultrafiltration membranes, particularly in a membrane bioreactor (MBR) system, effectively remove heavy metals such as Co, Ni, Mn, and Sr, with effluent pH consistently ranging from 8.0 to 8.1 Recent advancements in ultrafiltration technology have significantly enhanced permeability, enabling operations at lower transmembrane pressures, as low as 7 KPa (1.01 psi) A study reported the successful treatment of paper mill wastewater using an integrated membrane process that combines MBR, continuous membrane filtration (CMF), and reverse osmosis (RO), addressing the limitations of conventional treatment methods that fail to meet the stringent water quality requirements of the paper-making industry The initial discharge from the sedimentation tank underwent treatment through an anoxic/aerobic/MBR membrane system to effectively remove NH3–N and dissolved organic compounds.
Aerobic treatment involves the use of free or dissolved oxygen by microorganisms, known as aerobes, to degrade organic waste efficiently This process accelerates biodegradation by utilizing oxygen as an electron acceptor, which enhances the throughput capacity of treatment systems Among various biological treatment methods, the activated sludge process is the most prevalent, exhibiting similar organic loading rate distributions Activated sludge plants, particularly those treating effluent from pulp and paper mills, demonstrate high removal efficiencies for biochemical oxygen demand (BOD) and chemical oxygen demand (COD) For instance, aerobic cultures from the Ankara Municipal Wastewater Treatment Plant in Turkey achieved a sludge age of 2.8 days and an organic loading of 165,000 kg BOD5/day, showcasing the effectiveness of this treatment approach.
Recent studies have demonstrated that a two-stage activated sludge process significantly enhances the removal of biochemical oxygen demand (BOD) and soluble chemical oxygen demand (COD) By incorporating Floobeds (floating biological beds) in series, the removal rates improved from 51% to 90% for COD and 70% to 93% for BOD Microorganisms such as Pseudomonas putida, Citrobacter sp., and Enterobacter sp have shown effectiveness in eliminating color, BOD, COD, phenolics, and sulfide within this process Additionally, the treatment of chlorinated phenols, 1,1-dichlorodimethyl sulfone (DDS), and chlorinated acetic acids has been successfully reported, achieving a removal efficiency of 90% for BOD7, 70% for COD, 40–60% for adsorbable organic halides (AOX), and 60–95% for chlorinated phenols in the activated sludge system.
EXPERIMENT
Research objective
The study aims to develop an effective wastewater treatment technology for pulp and paper mills in Vientiane, focusing on several specific objectives First, it will assess the current environmental challenges related to pulp and paper mill wastewater in Vientiane Second, the study will identify and evaluate suitable analytical methods for monitoring and controlling experimental processes Third, it will explore the potential of physicochemical methods for pretreating pulp and paper mill wastewater Additionally, the research will examine the effectiveness of biological treatment using activated sludge and a combined aerobic and anaerobic circulatory system for wastewater pretreatment Finally, the study will propose a comprehensive model for wastewater management within the pulp and paper industry in Vientiane.
Equipment and Chemicals
The study utilized advanced analytical equipment in the environmental chemistry laboratory to measure the quantity of substances in wastewater samples An Adventurer TM OHAUS analytical balance from Sweden was employed to accurately weigh chemical materials, while the Themoreactor TR320 facilitated precise temperature control during experiments.
( Germany) is performed to analyse heating of COD The
Coagulation/Floculation tests were performed in a jar test device Flocculate SW6 ( Arm field, UK) was evaluated by means of the COD and suspended solids reduction yieds Aerobic
Digester W11 ( Arm field, UK) is used for growing up the micoorganism and treated for reducing COD.
Figure 6 Diagram of Aerobic system W11
- K2Cr2O7 solution: dissolve 12.259 g of K2Cr2O7 (primary standard grade), which is previously dried at 103 o C in 2 h in distilled water and dilute to 1000 mL.
- Sulfuric acid reagent (H2SO4): add 5.5 g of silver sulfate (Ag2SO4) and 33.3g of sulfuric acid to distilled water and wait for the total dissolution 1-2 days.
- Borate buffer solution: add 88 ml of 0.1N NaOH solution to 500 ml of approximately 0.025M sodium tetra borate solution (9.5 g Na2B4O7.10 H2O/L) and dilute to 1 L.
Analitycal methods in the study
1 g of N-(1-naphthyl)-ethylenediamine dihydrochloride and stir to dissolve, then dilute to 1 L with water Solution is stable for about a month when stored in a dark bottle in refrigerator.
- Sodium oxalate, 0.025M (0.05N): dissolve 3.350 g of Na2C2O4 (primary standard grade) in water and dilute to 1000 ml.
- Ferrous ammonium sulfate, 0.05M (0.05N): dissolve 19.607 g of Fe(NH4)2
(SO4)2.6H2O and 20 ml of H2SO4 in water and dilute to 1000 ml Standardize. Stock nitrite solution: Commercial reagent-grade NaNO2 assays at less than 99%.
To prepare phosphorus solutions, start with Solution A by dissolving 25g of ammonium molybdate \((NH4)6MoO4\) in 300mL of distilled water, stirring gently For Solution B, mix 1.25g of ammonium vanadate \((NH4VO3\) in 300mL of distilled water, applying slight heat to aid dissolution.
NH4VO3 until completely dissolved.
2.3.Analytical methods in the study
2.3.1 Determination of Chemical Oxygen Demand
Chemical Oxygen Demand (COD) determination is based on the oxidation of organic matter using a boiling mixture of chromic and sulfuric acids In this process, a sample is refluxed in a strong acid solution of potassium dichromate (K2Cr2O7), leading to the conversion of organic compounds into carbon dioxide and water.
Cn H aObNc – dCr O 2- + (8d + c)H + → nCO2 + a+8d−3c H2O +cNH4 + 2dCr 3-
The oxidation of water is achieved using K2Cr2O7 in conjunction with silver sulfate The optimal amount of K2Cr2O7 is determined by measuring the produced concentration of Cr 3+ ions The level of green Cr 3+ ions is quantified through photometric analysis.
Experiment procedures of COD measurement
In a series of glass procedures, 1000 ml of wastewater was mixed with distilled water, followed by the introduction of 2.5 ml of the wastewater sample into a clean cuvette To this, 1.5 ml of silver sulfate was added, and after thorough mixing, 3.5 ml of sulfuric acid reagent was incorporated The mixture was then refluxed at 150°C for 2 hours to prevent overheating After cooling, the absorbance was measured at 605 nm using a spectrophotometer, as detailed in Table 6 and Figure 7 of the COD standard curve.
Table 6 Data of standard curve
Figure 7 COD standard curve 2.3.2 Determination of Biochemical Oxygen Demand
The biochemical oxygen demand (BOD) test is an empirical method that employs standardized laboratory procedures to assess the oxygen requirements of wastewater, effluents, and polluted water This test is primarily used to measure the waste load entering treatment plants and to evaluate the efficiency of BOD removal in various treatment systems.
The test evaluates the molecular oxygen consumed during a designated incubation period for the biochemical breakdown of organic materials, reflecting carbonaceous demand Additionally, it assesses the oxygen utilized for the oxidation of inorganic substances, including sulfides and ferrous iron, as well as the oxygen required to oxidize reduced nitrogen compounds.
(nitrogenous demand) unless their oxidation is prevented by an inhibitor The seeding and dilution procedures provide an estimate of the BOD at pH values in the range of 6.5 to 7.5.
Lenore S Clesceri, Arnold E Greenberg, and Andrew D Eaton describe various methods for measuring oxygen demand, including the 5-day biochemical oxygen demand (BOD5) and definitive BOD, which involves oxygen consumption measurements taken after 60 to 90 days of incubation Additionally, they highlight the respirometric method for continuous oxygen uptake and note that there are numerous variations in oxygen demand measurements, utilizing both shorter and longer incubation periods.
Oxygen uptake rates can be assessed through absorption tests, allowing for the selection of alternative seeding, dilution, and incubation conditions that replicate receiving-water environments This approach offers a valuable estimate of the environmental impacts of wastewaters and effluents.
The BOD was tested in Refrigerated Incubator VELP Model FTC9.
The determination of ammonia levels is influenced by two key factors: concentration and the presence of interferences Typically, direct manual measurement of low ammonia concentrations is limited to drinking water, clean surface water, groundwater, and high-quality nitrified wastewater effluents For accurate results, dissolve 50 g of potassium sodium tartrate (KNaC4H4O6) in the testing solution.
To determine ammonia nitrogen concentrations, a series of visual standards were prepared in Nessler tubes by adding 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 ml of standard NH4Cl solution and diluting to 50 ml with water The standards and distillate portions were then Nesslerized by adding 0.5 ml of Nessler reagent, followed by the addition of 0.2 ml of xenhet reagent, resulting in a brown color that is strongly adsorbed in the 400-425 nm wavelength range A standard curve was generated by varying ammonia concentrations and measuring corresponding absorbance values, allowing for the accurate determination of ammonia nitrogen concentrations in the range of 0.4 to 5 mg/L.
Table 7 Data of ammonia standard curve
2.3.4 Analysis of Nitrite and Nitrate a Determination of Nitrite
Nitrite (NO2 –) analysis involves turbidity removal from samples containing suspended solids Begin by neutralizing 50 ml of a clear sample to pH 7 Prepare a series of visual color standards in Nessler’s tubes by adding varying volumes of a standard NO2 – solution (0 to 1 ml) and diluting each to 50 ml with water Next, incorporate 1 ml of sulfanilamide solution and allow the reaction to proceed for 2 to 8 minutes Follow this by adding 1 ml of NED dihydrochloride solution, mixing immediately, and allowing the mixture to stand for at least 10 minutes Finally, conduct photometric measurements at a wavelength of 543 nm, as detailed in table 8 and figure 12.
Table 8 Data of nitrite standard curve making
Figure 9 Nitrite standard curve b Determination of Nitrate
The UV absorption is carried out at 220 nm which enables the rapid determination of NO3 - Because dissolved organic matters also may absorb at 220 nm and
NO3- does not absorb light at 275 nm, but a second measurement at this wavelength can be utilized to adjust the NO3- value The degree of this empirical correction depends on the type and concentration of organic matter present, which can differ between various water sources.
This method is not advisable for situations requiring a substantial correction for organic matter absorbance However, it can be effective for monitoring NO3- levels in water bodies with consistent organic matter types.
Correction factors for organic matter absorbance can be determined by combining the analysis of original NO3 - content through an alternative measurement To eliminate potential interference from suspended particles, sample filtration is performed Additionally, acidification with 1N HCl is implemented to mitigate interference from hydroxide or carbonate concentrations of up to 1000 mg CaCO3/L, while chloride does not affect the determination process.
The standard curve making: using pipette to take NO3 - solution into the volumetric glass 25ml The result is shown as follow.
Table 9 Data of nitrate standard curve
Figure 10 Nitrate standard curve 2.3.5 Procedure for the determination of Phosphate
PO4 3- reacts with Vanadat – Molipdat in acidic environment, giving the yellow complex The Abs values depend on the amount of PO4 3- and measured at 470nm.
The standard curve is built based on the concentration of PO4 3- - P and the light absorbance The concentration of PO4 3- - P varies from 0 to 18 mg/L as shown in table
10 Take 3ml of phosphate reagent to the volumetric glass 25 ml then add standard solution and accurate to the level line Shaking and measuring at the wavelength of 470nm.
Table 10 Data of phosphorus standard curve
Preparation of Pulp and paper mill samples
Wastewater samples were collected from two locations in Vientiane's Asia paper mill and one from the Huu Nghi paper factory in Hoa Binh province Sample 1, taken from the final treatment tank, had an initial COD value of 3281 mg/L Sample 2, sourced from the effluent discharged into the pond, represented wastewater from the pink tissue paper production process with an initial COD value of 2140 mg/L In contrast, Sample 3 from the Huu Nghi paper factory exhibited a significantly higher initial COD value of 161740.36 mg/L.
Physicochemical method for the pretreatment of pulp and paper mill
2.5.1 Coagulation experiments of sample 1 and 2
In the optimal dosage experiments for COD removal using PAC, wastewater samples were prepared in six beakers of a Flocculator, with the pH adjusted to 2 Various volumes of a 10% PAC solution, ranging from 0.5 to 4.0 mL, were added The efficiency of using 2 mL of PAC for COD removal was calculated following the methodology outlined in section 2.4.
2.5.2 Reduction of COD value by pH change for sample 3
Sample 3 has initial black color, pH value of 13.5 and COD value of 161740.36 mg/L For this experiment, first the wastewater sample 3 was diluted to the COD value of 6469.61 mg/L and this solution was used to investigate the effect of pH on the reduction of COD in pulp and paper mill wastewater The experiments were carried out as follows: using diluted H2SO4 acid solution to adjust the pH of the diluted wastewater solution to reach the value of 1, 2 or 3; slowly stirring in 15 minutes at 40 rpm, settle the solution in
30 minutes; then the water layer in the top was determined COD value of 922.20 mg/L to this sample for combined aerobic and anaerobic circulatory system treatment in the next step.
“The water layer in the top which has the COD value of 922.20 mg/L was used for the combined aerobic and anaerobic circulatory system treatment in the next step”
2.6 The removal of COD in pulp and paper mill wastewater by combined Aerobic and Anaerobic Circulatory System
The system integrates both aerobic and anaerobic processes for wastewater treatment Initially, 60 liters of pre-treated wastewater is adjusted to a pH of 7 and pumped into the anaerobic column, where microorganisms in the porous film degrade organic compounds As the flow reaches the top of the anaerobic column, it is propelled directly into the aerobic column due to pressure balance In the aerobic column, air is supplied through a pumping mechanism to create optimal conditions for microbial activity, further degrading organic matter Effluent quality is monitored at the outlet, with periodic sampling to measure COD, ammonia, nitrite, nitrate, and phosphorus concentrations, while maintaining a dissolved oxygen (DO) level of approximately 0.5 mg/L for effective aerobic treatment.
Figure 12 Diagram of combined anaerobic and aerobic system
The draught column serves as a compact treatment unit integrating both anaerobic and aerobic activated sludge processes, primarily evaluated for its nitrogen removal efficiency Within this system, the draught tube functions as an aerobic zone, while the annulus acts as an anaerobic zone Wastewater is first introduced into the upper section of the annulus, where it undergoes anaerobic treatment, before being lifted into the draught column's aerobic zone through air lift action The treated effluent is then discharged from the top of the column, utilizing particles with a diameter ranging from 0.3 to 0.5 cm, which provide a large specific surface area of approximately 700-800 m².
The treated material is non-toxic to microorganism growth, as demonstrated by SEM (scanning electron microscope) images that illustrate the changes in surface structure before and after treatment Below, the surface structure of the porous material is presented.
Figure 13 Surface of porous material
Over several days of circularly pumping, we varied the volumes of wastewater added to the tank, starting from 15 ml to 20 ml After multiple cycles of nutrient water treatment, we focused on sample 3 Following the wastewater treatment, we analyzed the porous material using Scanning Electron Microscopy (SEM) The SEM images revealed changes in the porous material's surface, attributed to microorganism growth Specifically, the SEM image shown in figure 14 illustrates the porous material membrane after three cycles of nutrient-rich water pumping, while figure 15 indicates that the microorganisms present on the porous surface measured 125 μm in thickness post-treatment.
Material filling in column
The draught column serves as a compact treatment unit for both anaerobic and aerobic activated sludge processes, focusing on effective nitrogen removal Within this system, the draught tube functions as an aerobic zone, while the annulus operates as an anaerobic zone Wastewater is introduced into the upper portion of the annulus, allowing it to flow with sludge into the draught column through air lift action The treated effluent is then discharged from the top of the draught column, utilizing particles with a diameter ranging from 0.3 to 0.5 cm, which provide a large specific surface area of approximately 700-800 m².
The treated material is safe for microorganism growth, as demonstrated by the scanning electron microscope (SEM) images that reveal the surface structure changes of the porous material before and after treatment.
Figure 13 Surface of porous material
Over several days of circular pumping, we varied the volumes of wastewater added to the tank, starting from 15 ml and increasing to 20 ml After multiple cycles of nutrient water treatment, we focused on sample 3 for wastewater treatment Post-treatment, we analyzed the porous material using Scanning Electron Microscopy (SEM), revealing surface changes attributed to microorganism growth Figure 14 displays the SEM image of the porous material membrane following three cycles of nutrient-rich water pumping, while Figure 15 illustrates that the thickness of the microorganisms on the porous surface reached 125 μm after treatment.
Figure 14 Membrane of porous material after three times circularly pumping water containing nutrient
RESULTS AND DISCUSSION
Pretreatment of pulp and paper mill wastewater by physicochemical methods39 1 Coagulation experiments for sample 1 and 2
3.1.1 Coagulation experiments for sample 1 and 2
3.1.1.1 Effect of PAC dosage to sample 1
An experiment was conducted to evaluate the impact of PAC dosage on the removal efficiency of COD from pulp and paper mill wastewater, which initially had a COD value of 3281 mg/L Nine samples were treated with varying volumes of a 10% PAC solution, ranging from 0.5 to 4.0 mL After a light stirring period of 3-5 minutes, the samples were allowed to settle for 2 hours, and the resulting COD values were recorded The findings revealed that the optimal removal of COD occurred with a PAC dosage of 2.0 mL, reducing the COD to 846.76 mg/L Consequently, a dosage of 2.0 mL of PAC was selected for further experiments as the optimal condition.
Table 11 Effect of PAC dosage on COD reduction for sample 1
Figure 16 Diagram of effect of PAC dosage on COD reduction of sample 1
According to the experimental results, the optimal dosage of PAC is 2 mL of 10% solution per 100 mL of wastewater, or 2000 mg PAC per liter of wastewater.
3.1.1.2 Effect of PAC dosage to sample 2
The experiments conducted on wastewater sample 2 followed the same methodology as those for sample 1, with the results presented in Table 12 Consistent with sample 1, the use of 2 mL of 10% PAC solution yielded the highest reduction in COD levels.
The line graph indicates that as the volume of PAC (mL) exceeds 2 mL, there is a downward trend; however, this trend fluctuates slightly, remaining around 1%, suggesting a stable overall pattern Thus, the optimal dosage of PAC can be inferred from this data.
2 mL of 10% solution per 100 mL of wastewater, or 2000 mg PAC per liter of wastewater After using PAC with volume of 2.0 mL, COD was decreased to 503.11 mg/L.
Table 12 Effect of PAC dosage on COD removal for sample 2
Figure 17 Diagram of effect of PAC dosage on COD removal 3.1.2 Effect of the pH and PAC dosage on the reduction of COD in sample 3
3.1.2.1 Effect of the pH to the reduction of COD
The sample 3 had initial black color, pH value of 13.5 and COD value of
In a study examining the impact of pH on the reduction of Chemical Oxygen Demand (COD) in wastewater, sample 3 was diluted to a COD value of 6469.61 mg/L A diluted sulfuric acid solution was added to three wastewater samples to lower the pH, followed by stirring for 2-3 minutes at 40 rpm and allowing the mixture to settle for 2 hours The resulting liquid phase was analyzed for COD values Results indicated that at a pH of 2, the highest COD removal efficiency was achieved at 62.16% In contrast, at pH 3, the removal efficiency decreased slightly to 62.01% Consequently, pH 3 was chosen for subsequent experiments.
CO D re m ov al (% ) pH 1 2 3
Table 13 Effect of pH on COD removal
Figure 18 Diagram of effect of pH on COD removal
3.1.2.2 Effect of the PAC dosage to the reduction of COD
After adjusting the pH to 3, the COD value measured 2457.8 mg/L, leading to the next step of coagulation with PAC Six samples were adjusted to a pH of 6 and treated with 0.5 to 3.0 ml of a 10% PAC solution These samples were stirred for 15 minutes at 40 rpm and allowed to settle for 30 minutes The findings, detailed in Table 14 and Figure 18, indicated that the optimal dosage of PAC was 2 ml of the 10% solution.
Table 14 Effect of coagulant PAC on COD removal
Figure 19 Diagram of effect of coagulant PAC on COD removal
The optimal volume of PAC for effective COD removal, as indicated by the diagram, is 2mL, achieving a maximum removal rate of 62.33% Increasing the PAC volume beyond 2mL resulted in a downward trend in COD removal, although fluctuations remained around 1%, suggesting a stable trend Consistent with samples 1 and 2, the ideal dosage of PAC for achieving optimal COD removal in sample 3 is determined to be 2000mg PAC/L.
Investigation of the biological treatment with activated sludge
3.2.1 Effect of retention time on COD removal for sample 1
Following the coagulation pretreatment, the sample exhibited a Chemical Oxygen Demand (COD) value of 846.76 mg/L, while the 5-day Biochemical Oxygen Demand (BOD5) was recorded at 450.00 mg/L, resulting in a BOD/COD ratio of 0.53 This ratio indicates a favorable condition for aerobic treatment Table 15 illustrates the relationship between COD removal efficiency and retention time during the treatment process.
Table 15 Data of effect of retention time on COD removal
Figure 20 Diagram of effect of retention time on COD removal
The line graph illustrates the trend in treatment effectiveness, showing an increase in COD removal over the reaction period At 7 hours, the COD value reached 199.66 mg/L, indicating that the wastewater sample requires additional treatment.
3.2.2 Effect of retention time on COD removal for sample 2
After the coagulation step, sample 2 had a COD value of 503.11 mg/L, and after 5 days, the BOD5 measured 297.00 mg/L This resulted in a BOD/COD ratio of 0.59, indicating that aerobic treatment is suitable for this sample, as noted by Rodriguez et al (2007) The influence of retention time on the COD removal for sample 2 is illustrated in Table 16 and Figure 21.
Table 16 Data of effect of retention time to COD removal
Figure 21 Diagram of effect retention time on COD removal
The line graph illustrates the treatment trend, showing an increase in COD removal over time After 7 hours, the COD level measured 48.66 mg/L, with color and pH at 7, all meeting the environmental release standards set by Lao and Vietnam industrial wastewater quality regulations in 2005.
3.2.3 Effect of retention time on COD removal for sample 3
To evaluate the COD removal efficiency of the activated sludge process, experiments were conducted on sample 3 from Laos, with the findings presented in Table 17 and Figure 22.
Primary investigation on the treatment of pulp and paper mill wastewater by
Table 17 Data of effect of aerobic on COD removal
Figure 22 Diagram of effect of aerobic on COD removal
At the time of 7 hours the COD value was 524.55mg/L The wastewater sample should go to further treatment methods.
3.3.Primary investigation on the treatment of pulp and paper mill wastewater by the combination of circulatory aerobic and anaerobic system
After pretreatment involving pH adjustment and coagulation, wastewater sample 3, with a COD value of 922.2 mg/L, was utilized to assess treatment efficiency in a circulatory aerobic and anaerobic system A total of 60 liters of wastewater were adjusted to a pH of 7-8 and transferred to the first column filled with porous film, where microorganisms degraded the organic compounds Analytical samples were collected to evaluate COD values.
The results showed that after 57 hours the COD removal was 94.99% which reduced COD value from 922.20 mg/L to 46.2 mg/L The gained COD value was good for outflow standard.
Comparing the efficiency of aerobic systems to the combined circulatory system of aerobic and anaerobic processes (CSOCA&A), the latter demonstrates a significantly higher efficiency of 94.99% compared to 90% for aerobic systems alone In the anaerobic phase, the absence of oxygen facilitates the breakdown of persistent organic chemicals into more manageable forms, which can subsequently be treated effectively using aerobic methods.
Table 18 Data of effect of CSOCA&A on COD removal
Figure 23 Diagram of effect of aerobic to COD 3.3.2 The change of ammonia concentration
Monitoring the change of ammonia concentration, it was seen that ammonia reduced to 3.02 mg/L after 57 hours treated by CSOCA&A This is suitable for the output standard required.
Table 19 Data of effect of CSOCA&A to NH 4 + due to time.
Figure 24 Diagram of effect of aerobic to Ammonia 3.3.3 The change of nitrite concentration
Nitrite and nitrate concentrations were analyzed to assess nitrogen levels and the behavior of nitrogen compounds under CSOCA&A conditions During the two-hour observation, nitrite peaked at 12.46 mg/L, followed by a significant reduction of 94.6% over the subsequent 46 hours.
Table 20 Data of effect of CSOCA&A on NO 2 - due to time
Am on ia C on ce nt ra tio n( m g/ L)
Figure 25 Diagram of effect of aerobic on Nitrite concentration
3.3.4 The change of nitrate concentration
Over 46 hours the nitrate reduction was 77.4% and the output standard for nitrate was hopeful to release.
Table 21 Data of effect of CSOCA&A on Nitrate due to time
Figure 26 Diagram of effect of aerobic on Nitrate 3.3.5 The change of phosphorus concentration
N itr at e Co nc en tr ati on (m g/ L) N itr ite C on ce nt ra tio n( m g/ L)
The amount of phosphorus over 46 hours was reduced from 23.10 mg/L to 9.3 mg/L This concentration has met the standard to release to the environment (wastewater discharge standard 2005 VN).
Table 22 Data of effect of CSOCA&A on phosphorus due to time
Figure 27 Diagram of effect of aerobic on phosphorus
The analysis of COD values, along with the total concentrations of nitrogen and phosphorus, indicates that the treated effluent meets the environmental release standards set by Lao and Vietnam's industrial wastewater quality standards of 2005.
3.3.6 A proposed model for pulp and paper mill wastewater treatment for Vientiane factories
A proposed model for treating wastewater from pulp and paper mills in Vientiane factories involves several key steps Initially, the wastewater is equalized and diluted to optimal conditions, followed by pH adjustment to 3 using diluted sulfuric acid The sludge generated is converted into solid form for subsequent treatment Next, the liquid phase's pH is raised to 6 and coagulated with a 10% PAC solution to effectively remove suspended solids and decrease COD levels The resulting sludge is again transformed into solid form for further processing, while the treated liquid proceeds to the next stage of treatment.
Ph os ph or us Co nc en tr ati on (m g/ L)
Sludge press Coagulation (pH=6) step Finally, all so used above wastewater samples were pumped to combined anaerobic and aerobic system.
Figure 28 A proposed models for pulp and paper mill wastewater treatment system for
Pulp and paper mill wastewate r
During the time of doing master thesis at Lab of Environmental Chemistry, Hanoi University of Science I have some conclusions as follows:
1 The current environmental issues in Vientiane in general and the pulp and paper mill wastewater in particularly were evaluated It is obvious that the environmental issues in Vientiane are becoming serious and urgently require the attention of the government as well as relative agencies.
2 The selected analytical methods are suitable for monitoring the value of COD, BOD and NH4 +, NO2 -
, NO3 -, PO4 3- contents in pulp and paper mill wastewater in Vientiane.
3 The application of physicochemical method to pretreat pulp and paper mill wastewater by adjusting the pH value to 2 and coagulating high suspended solids with 10% PAC solution is suitable for tissues paper factory in Vientiane.
4 The preliminary results of using the combined Aerobic and Anaerobic circulatory system for the pretreatment of pulp and paper mill wastewater have shown that the combined system gets higher efficiency of COD removal (94.99%) and than the aerobic one (90%).
5 A model for the wastewater management of pulp and paper mill industry inVientiane is proposed and will be evaluated for further application.
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