Coagulation-sedimentation Process Research Articles

Removal of particulate matter and dissolved organic matter from sedimentation sludge water during pre-sedimentation process: Performances and mechanisms

Sedimentation sludge water (SSW), a prominent constituent of wastewater from drinking water treatment plants, has received limited attention in terms of its treatment and utilization likely due to the perceived difficulties associated with managing SSW sludge. This study comprehensively evaluated the water quality of SSW by comparing it to a well-documented wastewater (filter backwash water (FBW)). Furthermore, it investigated the pollutant variations in the SSW during pre-sedimentation process, probed the underlying reaction mechanism, and explored the feasibility of employing a pilot-scale coagulation-sedimentation process for SSW treatment. The levels of most water quality parameters were generally comparable between SSW and FBW. During the pre-sedimentation of SSW, significant removal of turbidity, bacterial counts, and dissolved organic matter (DOM) was observed. The characterization of DOM components, molecular weight distributions, and optical properties revealed that the macromolecular proteinaceous biopolymers and humic acids were preferentially removed. The characterization of particulates indicated that high surface energy, zeta potential, and bridging/adsorption/sedimentation/coagulation capacities in aluminum residuals of SSW, underscoring its potential as a coagulant and promoting the generation and sedimentation of inorganic-organic complexes. The coagulation-sedimentation process could effectively remove pollutants from low-turbidity SSW ([turbidity]0 < 15 NTU). These findings provide valuable insights into the water quality dynamics of SSW during the pre-sedimentation process, facilitating the development of SSW quality management and enhancing its reuse rate.

Optimum conditions for high-speed solid-liquid separation by ballasted flocculation.

In the ballasted flocculation, high-speed sedimentation of suspensions is achieved using a microsand as a ballast material and a polymer flocculant combined with microflocs made of polyaluminum chloride (PAC) as an inorganic coagulant. In this study, three turbid water samples containing kaolin clay (kaolin concentration: 20, 200, and 500 mg/L) were treated by coagulation-sedimentation and ballasted flocculation. The effects of pH and PAC dosage, which are the controlling parameters for coagulation, and the microsand (silica sand) and polymer dosages, which are the controlling parameters for ballasted treatment, on the treatment efficiency and floc settling velocity were examined. The floc settling velocity under the optimum conditions was 17 times higher than that of the conventional coagulation-sedimentation process using PAC. The turbidity was 0.54 turbidity unit (TU) (TU as the kaolin standard), and its removal efficiency was 99.7%. Furthermore, turbid water samples with different kaolin concentrations (20 and 500 mg/L) were treated via the ballasted flocculation. In this study, fundamental information on the optimization of each dosage condition of coagulant, ballast, and polymer and pH condition in ballasted flocculation was obtained, and the removal mechanisms under optimal, underoptimistic and overoptimistic conditions were proposed.

Destabilization of polystyrene nanoplastics with different surface charge and particle size by Fe electrocoagulation

Nanoplastics (NPs) discharged from wastewater could pose a major threat to organisms in aquatic environments. Effective removal of NPs by the current conventional coagulation-sedimentation process is not yet satisfactory. This study aimed to investigate the destabilization mechanism of polystyrene NPs (PS-NPs) with different surface properties and sizes (i.e., 90 nm, 200 nm, and 500 nm) by Fe electrocoagulation (EC). Two types of PS-NPs were prepared by a nanoprecipitation method using sodium dodecyl sulfate and cetrimonium bromide solutions to produce negatively-charged SDS-NPs and positively-charged CTAB-NPs. For both NPs, obvious floc aggregation from 7 μm to 14 μm was observed only at pH 7 with particulate Fe accounted for >90 %. At pH 7, Fe EC removed 85.3 %, 82.8 %, and 74.7 % of the negatively-charged SDS-NPs at small-, mid-, and large-sizes from 90 nm, 200 nm, to 500 nm, respectively. Small-size SDS-NPs(90 nm) were destabilized through physical adsorption on the surface of Fe flocs, while the main removal mechanism of mid- and large-SDS-NPs(200 nm and 500 nm) involved the enmeshment of large Fe flocs. Compared to SDS-NPs(200 nm and 500 nm), Fe EC performed similar destabilization behavior to two CTAB-NPs(200 nm and 500 nm), but it resulted in much lower removal rates of 54.8 % - 77.9 %. The Fe EC also exhibited no removal (<1 %) ability toward the small-size and positively-charged CTAB-NPs(90 nm) due to insufficient formation of effective Fe flocs. Our results provide insight into the destabilization of PS in nano-scale with different sizes and surface properties, which clarifies the behavior of complex NPs in a Fe EC-system.

A novel hybrid coagulation-intermittent sand filter for the treatment of dairy wastewater

An intermittent sand filter (ISF) is a simple and cost-effective treatment method that may be adopted on farms to treat dairy wastewater (DWW). However, the use of ISFs has been limited due to the large area required for treatment, and the risk of filter clogging and phosphorus (P) breakthrough, which decrease the operational lifetime. To overcome these limitations, this study uses a novel, pilot-scale coagulation-sedimentation process prior to loading ISFs with DWW. The performance and operational lifetime of this new hybrid coagulation-ISF system was compared to a conventional ISF system in a replicated outdoor pilot-scale experiment over a 43-wk study duration (covering an entire milking season on a farm in Ireland). The hybrid system was able to operate effectively at a higher hydraulic loading rate than a conventional ISF system. The effluent quality from the conventional ISF deteriorated over the timeframe of the study until clogging occurred, while the hybrid system continued to perform effectively without any evidence of clogging or P breakthrough. The hybrid system obtained removal efficiencies ≥99% for all measured water quality parameters (chemical oxygen demand, total suspended solids, total P, ammonium and turbidity), and complied with EU directives concerning urban wastewater treatment. Overall, the hybrid coagulation-ISF is a promising technology that requires a small area (75% reduction in footprint in comparison to a conventional ISF) and minimal operator input, and produces high effluent quality.

A novel hybrid coagulation-constructed wetland system for the treatment of dairy wastewater

Constructed wetlands (CWs) are a cost-effective and sustainable treatment technology that may be used on farms to treat dairy wastewater (DWW). However, CWs require a large area for optimal treatment and have poor long-term phosphorus removal. To overcome these limitations, this study uses a novel, pilot-scale coagulation-sedimentation process prior to loading CWs with DWW. This hybrid system, which was operated on an Irish farm over an entire milking season, performed well at higher hydraulic loading rates than conventional CWs, and obtained removal efficiencies ≥99 % for all measured water quality parameters (chemical oxygen demand, total nitrogen and phosphorus, total suspended solids and turbidity), which complied with EU directives concerning urban wastewater treatment. Overall, the hybrid coagulation-CW is a promising technology that requires a smaller area than conventional CWs and minimal operator input, and produces high effluent quality.

The effect of multivalent anions on removal of Titanium dioxide nanoparticles from drinking water sources by coagulation-sedimentation processes: Efficacy and mechanisms

Titanium dioxide nanoparticles (TiO2 NPs) are emerging potential hazard contaminants. There is a pressing need to understand TiO2 NPs removal from anions-spiked complex waters by coagulation-sedimentation (C/S) processes. In this study, we investigate impacts of Cl−, NO3−, SO42−, and PO43− on TiO2 NPs removal at circumneutral pHs by C/S processes. Little removal of TiO2 NPs was observed in the absence and presence of Cl− or NO3−. However, 93% and 82% of 10 mg/L TiO2 NPs were removed within 45 min as dosing 0.6 mM PO43− and 0.8 mM SO42−, respectively, at 10 mg/L polyaluminum chloride (PAC) and pHini. 6.2 in C/S processes, with pseudo-first-order rate constants of 0.098 ± 0.002 and 0.072 ± 0.001 min−1, respectively. Reaction rates in this work were several orders of magnitude faster than those in previous studies. Removal efficiencies of TiO2 NPs reached higher than 89% with a spike of multivalent anions in tap water, thereby exhibiting high practical implication potential. Additionally, the temporal evolution of total particle number and fractal dimension demonstrated that the presence of SO42− and PO43− improved the formation of denser spherical flocs and consequently precipitation rates mainly due to charge neutralization. Moreover, appropriate coagulants, optimized levels of PAC, SO42− and PO43−, and acidic pHs favored nanoparticle removal. Together, this work suggests that the presence of background water composition could facilitate nanoparticle removal in a C/S process.

Removal of ammonium and manganese from surface water using a MeOx filter system as a pretreatment process

ABSTRACT Residual aluminium from the coagulation–sedimentation process in the treatment of surface water can decrease the catalytic activity of a manganese co-oxide filter film (MeOx) used for ammonium and manganese removal. To solve this problem, a MeOx filter was used as a pretreatment process to filtrate source water directly before the coagulation and sedimentation treatment. The removal performance and the mechanism of change in the activity of MeOx were investigated. The experimental results indicated that the MeOx filter removed ammonium and manganese from surface water sources effectively, and its manganese removal activity was enhanced. The characteristics of MeOx were investigated via SEM, EDS, XPS, and the BET surface area. Analysis of the experimental results showed that the increase in the content of Al under this condition was much lower than that under treatment with the coagulation–sedimentation process. After long-term operation, the amount and surface area of MeOx coated on the filter sand increased significantly, leading to an increase in the catalytic activity. However, in cold water, the catalytic activity of MeOx decreased, and more Mn(II) was obtained on the surface of MeOx. Thus, the morphology of MeOx changed. Fortunately, when water temperature increases, the removal activity can recover immediately. By inactivating microorganisms and comparing the removal performance with that under other conditions, the MeOx activity of the pretreatment process is preserved effectively and no strengthening measures are required. This study will provide a new strategy for the use of the MeOx catalytic technology.

Removal of disinfection by-product precursors in drinking water treatment processes: Is fluorescence parallel factor analysis a promising indicator?

This work investigated the removal efficiency of disinfection by-product (DBP) precursors by different drinking water treatment processes and evaluated the feasibility of using fluorescence components removal as an indicator. A four-component (including tryptophan-like, protein-bound, tyrosine-like, and humic-like components) parallel factor analysis model was developed basing on 288 fluorescence excitation-emission matrices. Among all treatment processes, coagulation-sedimentation process showed the best performance, with mean removal ratios of 30% in total fluorescence intensity and 31% in total formation potential (FP) of DBPs, respectively. It preferentially removed humic-like component C4 (43%). Advanced treatment processes were less effective in comparison. Ozone and biological activated carbon (BAC) combined process reduced 20% of total fluorescence intensity, while ultrafiltration process reduced < 3%. Ozonation and BAC filtration preferentially removed free amino acids (i.e., C1 and C3) and protein-bound (i.e., C2) components, with mean removal ratios of 12% and 17%, respectively. Significant correlations (p < 0.01, double-tailed) were observed between four fluorescence components removal and FPs reduction of three trihalomethanes, dichloroacetonitrile (DCAN), and 1,1-dichloropropanone (1,1-DCP). Specifically, the correlation coefficients for three trihalomethanes and 1,1-DCP followed the order of C4 > C1 > C2 > C3, while the order for DCAN was C2 > C4 > C1 > C3.

Trace organic contaminants abatement by permanganate/bisulfite pretreatment coupled with conventional water treatment processes: Lab- and pilot-scale tests

Bisulfite-activated permanganate (PM/BS) process has proven to be a promising method for trace organic contaminants (TrOCs) abatement. However, to our knowledge, most previous studies on PM/BS process were limited in synthetic water at lab-scale. Hence, the performance of TrOCs abatement by PM/BS process was investigated in real waters in this study, and for the first time, its feasibility as a pretreatment process was evaluated at pilot-scale. The lab-scale results indicated that almost all tested TrOCs could be completely removed from pure water, while their removal efficiencies varied widely from ∼20 % to ∼90 % in real waters. Correlation analysis suggested that TrOCs abatement decreased linearly with increasing concentration of dissolved organic matter (DOM) and halide ions in real waters. The TrOCs with electron-donating groups were more likely to be decomposed in PM/BS process. The PM/BS pretreatment produced MnO2 and decreased the aromatic signal of the DOM, which enhanced the removal of DOM during subsequent coagulation-sedimentation processes. Comparing with ozonation, chlorination, and permanganate processes, PM/BS process showed some advantages in terms of TrOCs abatement and operating costs. Furthermore, the pilot-scale experiment confirmed that PM/BS process combined with traditional water treatment processes could achieve excellent TrOCs abatement (greater than 84%).

Feasibility of Reuse Filter Backwash Water as Primary/Aid Coagulant in Coagulation–Sedimentation Process for Tertiary Wastewater Treatment

The purpose of this study is to evaluate the feasibility of reusing filter backwash water (FBWW) from the water treatment plant as a substitute for conventional coagulants (primary coagulant) and coagulant aid with aluminum sulfate (Al2(SO4)3) in the coagulation–sedimentation process as tertiary treatment urban effluents for reuse. The impact of reuse filter backwash water has been studied on the water quality in coagulation process. The analysis Fourier Transform Infrared showed the presence of Al(OH)3 in the filter backwash water. The results showed a very good performance of turbidity and organic matter removal by FBWW in both cases. For a dose of 22.5 mg Al/L of FBWW as primary coagulant, the removal of turbidity and UV254 absorbance was significant, with percentages of 65.8% and 31.7%, respectively, during the treatment of the secondary effluent. The best results were obtained for a neutral pH. With FBWW as coagulant aid, the optimal dose of Al2(SO4)3 decreased from 9.5 to 6.3 mg Al/L with better percentages of turbidity reduction and UV254 of 92.9 and 71.4%. This study permits to reduce the coagulant concentration.

Distribution of odor and taste compounds in the lakes and reservoirs of Pearl River Delta and the removal efficiency in source discharges

采用固相微萃取-气质联用技术对珠江三角洲9个城市共48个湖库水体中的土臭素（GSM）、2-甲基异茨醇（MIB）和2，3，6-三氯苯甲醚（TCA）等5种嗅味物质进行检测，并探讨污水处理厂和自来水厂处理工艺中嗅味物质的浓度变化规律，同时研究强化混凝沉淀工艺对嗅味物质的去除效果.结果表明：珠江三角洲湖库水体中嗅味问题最严重的是广州、佛山、肇庆、东莞、惠州和深圳6个城市，各市湖库的嗅味物质平均浓度为70.93~116.61 ng/L；中山、珠海与江门3个城市的嗅味问题不明显，各市湖库的嗅味物质平均浓度为22.78~58.82 ng/L；珠江三角洲的湖库中浓度最高的嗅味物质是MIB、TCA和GSM，这3种嗅味物质占了嗅味物质总浓度的80.18%~100.00%；污水处理厂和自来水厂中的处理工艺对嗅味物质均有一定的去除效果，嗅味物质的去除主要发生在混凝沉淀阶段；污水处理厂对MIB、TCA和GSM的平均去除率分别为53.55%、57.40%和72.90%；自来水厂对MIB、TCA和GSM的平均去除率分别为64.14%、69.63%和36.86%；强化混凝沉淀实验中，当嗅味物质初始浓度为200 ng/L时，Al₂O₃投加量为13.75 mg/L可使得混凝沉淀工艺对嗅味物质的去除效果最佳且保证铝盐不超标，嗅味物质浓度增大时Al₂O₃投加量也需增大；反应体系的pH值处于5~8时，混凝沉淀工艺对嗅味物质的去除效果最佳；混凝搅拌速率越快，嗅味物质的去除率越高且越快达到稳定.;With the continuous improvement of people's living standards, residents put forward higher requirements for water quality, and pay more attention to odor and taste problem. Concentrations of odor and taste compounds in 48 lakes and reservoirs of 9 cities in Pearl River Delta were detected with the method of Solid Phase MicroExtraction-Gas Chromatography/Mass Spectrometry (SPME-GC/MS) technique. The changes of odor and taste compounds concentrations along the water treatment processes of wastewater treatment plants and water supply plants, as well as the removal effect of odor and taste compounds by enhanced coagulation-sedimentation process were studied. The results showed that:the most serious stench problem was the lakes and reservoirs of Guangzhou, Foshan, Zhaoqing, Dongguan, Huizhou and Shenzhen. The average concentrations of odor and taste compounds in the lakes and reservoirs of these 6 cities were from 70.93 to 116.61 ng/L. And the stench problem was not obvious in the lakes and reservoirs of Zhongshan, Zhuhai and Jiangmen. The average concentrations of odor and taste compounds in the lakes and reservoirs of these 3 cities were from 22.78 to 58.82 ng/L. 2-methylisoborneol (MIB), 2,3,6-trichloroanisole (TCA) and Geosmin (GSM) were the main odor and taste compounds in all lakes and reservoirs, which accounted for 80.18%-100.00% of total odor and taste compounds. The water treatment progresses of wastewater treatment plants and water supply plants could considerably remove odor and taste compounds. Coagulation-sedimentation process had the greatest contribution to the removal of odor and taste compounds. In the wastewater treatment plants, the average removal rates of MIB, TCA and GSM were 53.55%, 57.40% and 72.90%, respectively. In the water supply plants, the average removal rates of MIB, TCA and GSM were 64.14%, 69.63% and 36.86%, respectively. In the enhanced coagulation-sedimentation experiment, for the initial concentrations of odor and taste compounds of 200 ng/L, coagulation-sedimentation process could reach the greatest removal effect of them, and aluminum was not excessive as well when the coagulant (Al₂O₃) dosage was 13.75 mg/L. When the concentrations of odor and taste compounds increase, the dosage of Al₂O₃ should increase, too. When the pH value of the reaction system was between 5 and 8, coagulation-sedimentation process could reach the greatest removal effect of odor and taste compounds. The faster the stirring rate of coagulation was, the higher the removal rate of odor and taste compounds reached, and the faster the stability reached.

Assessment of coagulation‐ultrafiltration performance for the treatment of primary wastewater using alum sludge

AbstractThe main purpose of this research was to develop an effective and inexpensive pretreatment for ultrafiltration (UF) membrane process in order to treat a primary effluent for its reuse in several applications by avoiding biological treatment. For that the impacts of reuse alum sludge liquid recovered by the drinking water treatment plant of Boudouaou (Algiers area) has been examined on the water quality in coagulation–sedimentation processes. The tests were carried out on a primary effluent of wastewater treatment plant. The elemental analysis by x‐ray fluorescence showed that the tested sludge is composed mainly of Al2O3 (41%) and SiO2 (44%). The efficiency of alum sludge as primary coagulant was compared with a conventional metal‐ion coagulant (fresh alum) using a jar test apparatus for simultaneous removals of turbidity, UV254 and chemical oxygen demand (COD). For dose of 30 mg Al/L, the sludge was effective as primary coagulant for removing the turbidity, COD and UV254.

Removal of Microcystis aeruginosa by UV/chlorine process: Inactivation mechanism and microcystins degradation

Inactivation of Microcystis aeruginosa by UV/chlorine process was investigated in this study. Chlorine decay with or without the presence of algal cells was modeled based on a kinetic model, and the second-order rate constant between chlorine and algal cells was determined to be 3.3 × 10−4 (mgC/L)−1 s−1. Flow cytometry as well as confocal laser scanning microscopy were used to characterize the cell integrity of M. aeruginosa. Results demonstrated that UV/chlorine pre-oxidation was responsible for the inactivation of M. aeruginosa, and the inactivation efficiency increased with the increasing dosage of chlorine. UV/chlorine process can significantly change the surface characteristics of M. aeruginosa and enhance the coagulation efficiency. Moreover, due to the destruction of algal cells, microcystin-LR would be released and then degraded during pre-oxidation, and the releasing endotoxin could be removed during subsequent coagulation-sedimentation process. This study suggests that UV/chlorine process might be a potential alternative for the pretreatment of cyanobacterial cells in treating cyanobacteria-laden water.

Pepper mild mottle virus as a process indicator at drinking water treatment plants employing coagulation-sedimentation, rapid sand filtration, ozonation, and biological activated carbon treatments in Japan.

To assess the potential of pepper mild mottle virus (PMMoV) as a viral process indicator, its reduction through coagulation-sedimentation (CS) and rapid sand filtration (RSF) were compared with those of Escherichia coli, previously used viral indicators, and norovirus genotype II (NoV GII; enteric virus reference pathogen) in a bench-scale experiment. PMMoV log10 reductions in CS (1.96 ± 0.30) and RSF (0.26 ± 0.38) were similar to those of NoV GII (1.86 ± 0.61 and 0.28 ± 0.46). PMMoV, the most abundant viruses in the raw water, was also determined during CS, RSF, and advanced treatment processes at two full-scale drinking water treatment plants under strict turbidity management over a 13-month period. PMMoV was concentrated from large-volume water samples (10-614 L) and quantified by Taqman-based quantitative polymerase chain reaction. The PMMoV log10 reduction in CS (2.38 ± 0.74, n = 13 and 2.63 ± 0.76, n = 10 each for Plant A and B) and in ozonation (1.91 ± 1.18, n = 5, Plant A) greatly contributed to the overall log10 reduction. Our results suggest that PMMoV can act as a useful treatment process indicator of enteric viruses and can be used to monitor the log10 reduction of individual treatment processes at drinking water treatment plants due to its high and consistent copy numbers in source water.

Distribution of perfluorinated compounds in drinking water treatment plant and reductive degradation by UV/SO32- process.

Perfluorinated compounds (PFCs), which are widely used in industrial and residential areas, have a large negative impact on the environment. This study investigated the removal efficiency of five PFCs in a drinking water treatment plant. The results indicate that the total PFC concentration in raw water is 261.51ngL-1 and that perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are the predominant pollutants. Among all of the treatment processes, coagulation sedimentation process had the highest removal ratio of PFCs (36.12%), and removal ratio was the least in the sand filtration process. The ozonation/activated carbon and disinfection processes increased the concentration of PFCs. Therefore, developing an effective treatment to degrade PFCs is feasible. In this study, we proposed a method using UV irradiation of SO32- at 365nm to degrade PFCs. The SO32- concentration, pH, and initial concentration had profound impacts on the degradation of PFCs. When the PFC initial concentration was 20mgL-1, the SO32- concentration was 2.4gL-1, and in the presence of buffer, the degradation of PFCs was the most efficient, with the degradation ratio close to 100% after 60min of reaction. During the degradation of PFCs, short-chain PFCs and hydrofluorinated carboxylic acid were generated. From the above, we proposed a detailed mechanism of degradation and its possible pathways.

Tracking changes in composition and amount of dissolved organic matter throughout drinking water treatment plants by comprehensive two-dimensional gas chromatography–quadrupole mass spectrometry

Dissolved organic matter (DOM) can affect the performance of water treatment processes and produce undesirable disinfection by-products during disinfection. Several studies have been undertaken on the structural characterization of DOM, but its fate during drinking water treatment processes is still not fully understood. In this work, the nontargeted screening method of comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC×GC-qMS) was used to reveal the detailed changes of different chemical classes of compounds in DOM during conventional and advanced drinking water treatment processes at three drinking water treatment plants in China. The results showed that when the dissolved organic carbon removal was low, shifts in the DOM composition could not be detected with the specific ultraviolet absorbance at 254nm, but the changes were clear in the three-dimensional fluorescence excitation-emission matrix or GC×GC-qMS analyses. Coagulation-sedimentation processes selectively removed 37–59% of the nitrogenous compounds, alcohols and aromatic hydrocarbons but increased the concentrations of halogen-containing compounds by 17–26% because of the contact time with chlorine in this step. Filtration was less efficient at removing DOM but preferentially removed 21–60% of the acids. However, other organic matter would be released from the filter (e.g., nitrogenous compounds, acids, and aromatic hydrocarbons). Biological activated carbon (BAC) treatment removed most of the compounds produced from ozonation, particularly ketones, alcohols, halogen-containing compounds and acids. However, it should be noted that certain highly polar or high molecular weight compounds not identified in this study might be released from the BAC bed. After the whole treatment processes, the concentrations of nitrogenous compounds, alcohols, alkenes, aromatic hydrocarbons and ketones were decreased more by the advanced treatment processes than by the conventional treatment processes. Alcohol and ketone removals were probably related to the reduction in protein-like materials. Alkane removal was probably related to the reduction in fulvic acid-like and humic acid-like materials.

Removal of Suspended Solids in Anaerobically Digested Slurries of Livestock and Poultry Manure by Coagulation Using Different Dosages of Polyaluminum Chloride

In this study, anaerobically digested slurries of livestock and poultry manure were pretreated by coagulation-sedimentation using an inorganic polymer coagulant, polyaluminum chloride (PAC). The effect of different PAC dosages on suspended solids (SS) removal and pH in the biogas slurries was assessed to provide reference values for reducing the organic load of biogas slurry in the coagulation-sedimentation process and explore the feasibility of reducing the difficulty in subsequent utilization or processing of biogas slurry. The results showed that for the pig slurry containing approximately 5000 mg/L SS, the removal rate of SS reached up to 81.6% with the coagulant dosage of 0.28 g/L PAC. For the chicken slurry containing approximately 2600 mg/L SS, the removal rate of SS was 30.2% with the coagulant dosage of 0.33 g/L PAC. The removal rate of SS in both slurries of livestock and poultry manure exhibited a downward trend with high PAC dosage. Therefore, there is a need to control the PAC dosage in practical use. The pH changed little in the two types of biogas slurries after treatment with different PAC dosages and both were in line with the standard values specified in the “Standards for Irrigation Water Quality”.

Optimisation of contaminant removal in wet-weather sewage flows

A coagulation–sedimentation process with polyaluminium chloride (PAC) as a coagulant was used to treat wet-weather sewage flows with high concentrations of contaminants during the initial stages of a rainfall event. Response surface methodology and central composite design were applied to evaluate the optimal operating conditions of pH, turbidity and PAC dose to maximise simultaneous removal of contaminants at wastewater treatment plants. The optimal conditions were found to be a pH of 5, turbidity of 400 NTU and PAC dose of 48 mg/l. This resulted in the removal of 80·5% phosphorus, 79·8% chemical oxygen demand (COD) and 81·8% Escherichia coli. Under the assumption of wastewater with a neutral pH of 7, the optimal turbidity and PAC dose conditions resulted in the removal of 81·0% phosphorus, 76·7% COD and 64·5% E. coli.

Effect of cell integrity on algal destabilization by oxidation-assisted coagulation

A hybrid oxidation–coagulation process is commonly adopted to destabilize algae and subsequently improve the removal of algae from water through sedimentation and filtration in water treatment plants (WTPs). Preoxidation is crucial to improving algae removal by a coagulation–sedimentation process. The goal of this study was to investigate the effect of oxidation with NaOCl and ClO2 on the cell integrity of algae (i.e. diatoms) and the destabilization of algae by means of Alum coagulation. The effects of oxidation-assisted coagulation on the performance of sedimentation as well as filtration were evaluated. The results show that ClO2 reduces cell integrity more severely than NaOCl during oxidation. The degradation of chlorophyll a and humic-like substances generated by cells ruptured by ClO2 oxidation is stronger than that by NaOCl oxidation. During oxidation both NaOCl and ClO2 fail to cause significant cell lysis, while cell settleability can be improved markedly by using only ClO2. Preoxidation with ClO2 is more effective in destabilizing the particles and algae when applying Alum coagulation at low dosages. It was found that the residual algae counts in the supernatants are inversely well-correlated to its filterability instead of its residual turbidity. The reduced cell integrity resulting from ClO2 preoxidation effectively improves the performance of coagulation–sedimentation for algae (diatoms) removal and reduces the burden of filtration operation in the WTPs.

Combination of powdered activated carbon and powdered zeolite for enhancing ammonium removal in micro-polluted raw water

Even zeolite is promising in ammonia pollution disposing, its removal efficiency is frequently interfered by organics. As activated carbon has good removal efficiency on organic contaminants, combination of two adsorbents may allow their respective adsorption characteristics into full play. This paper provides a performance assessment of the combination for enhancing ammonium removal in micro-polluted raw water. Gel-filtration chromatography (GFC) was carried out to quantify the molecular weight (MW) range of organic contaminants that powdered activated carbon (PAC) and powdered zeolite (PZ) can remove. The polydispersity difference which also calculated from GFC may indicate the wider organic contaminants removal range of PAC and the relatively centralized removal range of PZ. The jar tests of combination dosing confirm a synergistic effect which promotes ammonium removing. Nevertheless, it also shows an antagonism hindering the due removal performance of the two adsorbents on CODMn, while it is not much evident on UV254. Furthermore, a comparison study with simulated coagulation–sedimentation process was conducted to evaluate the optimum dosing points (spatial and temporal) of PAC and PZ among follows: suction well, pipeline mixer, early and middle phase of flocculation. We suggest to dose both two adsorbents into the early phase of flocculation to maximize the versatile removal efficiency on turbidity, ammonium and organic contaminants.