Wastewater Treatment Units Research Articles

Hydrolysis of polyaluminum chloride prior to coagulation: Effects on coagulation behavior and implications for improving coagulation performance

The effects of polyaluminum chloride (PACl) hydrolysis prior to coagulation on both the coagulation zone and coagulation performance of a kaolin suspension were investigated by a novel jar test named the “reversed coagulation test”. The tests showed that PACl hydrolysis prior to coagulation decreased the performance of charge neutralization coagulation in the case of short-time slow mixing (10min; G=15sec−1) and increased the optimal dosage for charge neutralization and sweep coagulation. Moreover, the hydrolysis time had insignificant effects on the size and zeta potential of PACl precipitates and the residual turbidity of the raw water. However, PACl hydrolysis prior to coagulation and the size of PACl precipitates had a negligible effect on the performance of sweep coagulation. The results imply that, in practice, preparing a PACl solution with deionized water, rather than tap water or the outlet water from a wastewater treatment unit, can significantly save PACl consumption and improve the performance of charge neutralization coagulation, while preparing the PACl solution with tap or outlet water would not affect the performance of sweep coagulation. In addition, the optimal rapid mixing intensity appears to be determined by a balance between the degree of coagulant hydrolysis before contacting the primary particles and the average size of flocs in the rapid mixing period. These results provide new insights into the role of PACl hydrolysis and will be useful for improving coagulation efficiency.

Reverse osmosis concentrate conditioning for microalgae cultivation and a generalized workflow

Previous studies have demonstrated the feasibility of using wastewater as the nutrient source for microalgae cultivation. However, there is still a lack of guidance in wastewater conditioning to achieve optimum microalgae growth rate and complete N and P consumption in wastewater. In this study, a reverse osmosis concentrate (ROC) from the wastewater treatment unit of a dyeing company had been evaluated and conditioned for the phototrophic cultivation of Chlorella sp., with its toxicity, nutrient profile, salinity, pH and N/P ratio adjusted where necessary. After the wastewater was conditioned, Chlorella sp., which could not grow in the original ROC, achieved a growth rate comparable to that in an artificial medium. The percentages of N and P consumption were also balanced so that the nutrient utilization efficiency could be maximized. A generalized workflow and guidelines to develop wastewater conditioning plans for microalgae cultivation have also been proposed to guide the conditioning of wastewater streams for microalgae cultivation.

Characteristics and Source Apportionment of VOCs of High Pollution Process at Chemical Industrial Area in Winter of China

Online GC was adopted to monitor VOCs of high pollution process near a chemical industrial area in winter. PMF model was used to identify the major sources of VOCs and evaluate their contributions. The result showed that the main components during the period of observation were toluene, xylene, C3-C4 hydrocarbon and chloroform, etc. Organic sulfur compounds were the major odor pollutants at the chemical industrial area. The compounds including isobutane, n-butane, propane and acrylonitrile were enriched during two pollution periods. VOCs and NOx had the diurnal features of high concentration in the evening versus lower concentration during daytime, indicating the main influence from chemical industrial sources. While O3 had the diurnal features reflecting the photochemical reaction at chemical industrial area in winter. The PMF result showed that 48.0% of the total VOCs concentrations were attributed to synthetic materials industry, 24.0% to industrial organic sulfur process and wastewater treatment (including three sources), 14.7% to industrial organic solvent usage, and 13.3% to petrochemical process. So the wastewater treatment unit was a major source of odor pollution at chemical industrial area.

Evaluation of virus reduction efficiency in wastewater treatment unit processes as a credit value in the multiple-barrier system for wastewater reclamation and reuse.

The virus reduction efficiency of each unit process is commonly determined based on the ratio of virus concentration in influent to that in effluent of a unit, but the virus concentration in wastewater has often fallen below the analytical quantification limit, which does not allow us to calculate the concentration ratio at each sampling event. In this study, left-censored datasets of norovirus (genogroup I and II), and adenovirus were used to calculate the virus reduction efficiency in unit processes of secondary biological treatment and chlorine disinfection. Virus concentration in influent, effluent from the secondary treatment, and chlorine-disinfected effluent of four municipal wastewater treatment plants were analyzed by a quantitative polymerase chain reaction (PCR) approach, and the probabilistic distributions of log reduction (LR) were estimated by a Bayesian estimation algorithm. The mean values of LR in the secondary treatment units ranged from 0.9 and 2.2, whereas those in the free chlorine disinfection units were from -0.1 and 0.5. The LR value in the secondary treatment was virus type and unit process dependent, which raised the importance for accumulating the data of virus LR values applicable to the multiple-barrier system, which is a global concept of microbial risk management in wastewater reclamation and reuse.

Assessment of the Performance of Microbial Fuel Cell (MFC) for the Removal of Nitrate from Water

Nitrate ion, a pollutant and carcinogen in water, has been removed successfully in a microbial fuel cell with simultaneous generation of electricity in a lab scale. We used a system including two anode and cathode chamber to remove nitrate in the cathode chamber with generating energy by transferring electrons through an electrical circuit in ambient temperature. A voltage of 151 mV with an external resistance of 1000Ω observed where the maximum power density achieved was 1.375mW/m 2 with an external resistance of 800Ω. Seven days after the cell and without the presence of a catalyst, the amount of COD decreased by 25 percent. In addition, amount of nitrate decreased from 50 mg/L to 43mg/L. During 28 days of, daily removal of COD was 13 mg/L, and after this period of cell a significant decreasing of 78 percent was obtained for COD. Columbic efficiency of the process was reported to be 40 percent during 28 days that reflects the effectiveness of the system. In the presence of hexacyano ferrate as an excellent oxidant in the cathode the generated voltage were 4.5 times higher than when nitrate was used. This shows that nitrate can be successfully removed from water and wastewater treatment units with significant decrease in COD and generating electricity.

English

The aim of this study was to assess the removal efficiency of Escherichia coli at Mafisa and Mzumbe domestic wastewater treatment ponds in Morogoro, Tanzania. The study was done from October, 2013 to April, 2014. A total of 125 water samples from inlets and subsequent anaerobic, facultative and maturation ponds as well as treated wastewater were collected and analysed for E. coli. The estimated retention times of the wastewater treatment units were 19 and 22 days in Mafisa and Mzumbe ponds, respectively. The concentration of E. coli ranged from 4.70 to 5.60 log cfu/mL in untreated wastewater and was reduced to <1.00 to 2.00 log cfu/mL in the treated wastewater. During rainy and cold seasons, the effluent discharged out at Mafisa during August 2013; and March and April, 2014 was about 2 log cfu/mL while at Mzumbe E. coli concentration in effluent discharged out was up to 1.23 log cfu/mL. The concentration of E. coli in untreated and treated wastewater from the two wastewater treatment ponds study sites were comparable (P<0.05). Reduction of E. coli concentration in wastewater treatment ponds study sites was significant with less reduction seen at Mafisa, during rainy and cold seasons in March, April and August.  To conclude, the simple wastewater treatment ponds in the study sites were effective and demonstrated potential for reduction of public health risks associated with use of treated wastewater in agricultural irrigation and aquaculture.   Key words: Agricultural irrigation, aquaculture, retention time, wastewater treatment.

Reverse osmosis fouling during pilot-scale municipal water reuse: Evidence for aluminum coagulant carryover

Surfaces of two reverse osmosis (RO) membranes, one from each stage of a real-world pilot-plant operated in support of full-scale design of municipal water reuse, were extensively characterized to determine dominant foulants. Since the source wastewater was purified using extended aeration activated sludge, alum was also being added to the secondary clarifier to eliminate potential problems with colloidal sedimentation. Even though microfiltration (MF) was implemented to pretreat the secondary effluent prior to RO, significant aluminum fouling was detected by energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Peak shifts in Fourier transform infrared (FTIR) spectra and high resolution X-ray spectra indicated aluminum complexation with the membrane surface. Calcium and phosphorous (from added antiscalant) were also detected along with only weak signals from organic matter suggesting the dominance of inorganic fouling. These results demonstrate that chemicals added during wastewater reclamation can foul downstream membranes necessitating careful monitoring of existing wastewater treatment unit operations and RO pretreatment processes. One-step cleaning with EDTA at pH 11 successfully removed both aluminum and calcium and restored the flux to nearly that of the virgin membrane. In contrast, citric acid at pH 4 was effective in removing calcium but not aluminum and did not fully recover the flux. Hence, flux decline appears to be closely linked to aluminum rather than calcium deposition. Residues of EDTA and citric acid were detected on the cleaned membrane surface even following multiple rinse/washing cycles. Although this did not impact short-term flux recovery, the effects of such remnants on long-term membrane life and flux restoration following multiple cleaning cycles need further investigation.

Mathematical programming synthesis of non-isothermal water networks by using a compact/reduced superstructure and an MINLP model

The synthesis problems of non-isothermal water networks, combining heat exchanger network and water network (WN), usually consist of a significant number of constraints and variables, namely, flow rates, contaminant concentrations, temperatures and a large number of non-linear terms. In most cases, solving medium and large-scale synthesis problems is computationally too expensive and challenging. In order to circumvent that problem, we propose a compact superstructure and mixed-integer non-linear programming model for the simultaneous synthesis of non-isothermal WNs. The proposed superstructure includes heat integration stages enabling direct and indirect heat exchanges with a manageable number of hot and cold streams. This reduces the models size enabling easier solutions of the synthesis problems using local solvers. In addition, a superstructure reduction strategy is proposed making the superstructure flexible and adaptable for different types of problems, namely, pinched and threshold, and providing additional reduction of connections within the proposed superstructure. The proposed model is solved using a two-step solution strategy including initialisation and design steps. The model is applied to the examples of different complexities including single and multiple contaminant problems, and water-using and wastewater treatment units. Using the proposed iterative strategy, the improved locally optimal solutions are identified for most examples, minimising the total annual cost of the overall network.

Wastewater treatment challenges faced by the petrochemical and refinery industry, and opportunities for water reuse

Industrial wastewater differs from municipal wastewater. The limits for treated effluent discharge and targets for re-use are typically the same, and derived from the best available technology for municipal wastewater treatment. The main treatment unitary processes are also the same; although proper adaptation to specific, different, industrial wastewater streams is needed. This paper provides some examples of the challenges presented by specific wastewater sources (high total dissolved solids, high temperature, spent caustic, etc.), lack of previous similar experience – e.g., using membrane bioreactors for refinery wastewaters, and/or absorption chillers, and plate and frame heat exchangers) or to legislation protecting sensitive environments (limits on total nitrogen or soluble metals). The methods by which these were faced and overcome to achieve treatment and/or re-use standards are described. General water cycle optimization issues around industrial facilities with appropriate use of existing wastewater treatment units are also discussed, as well as selecting between treated municipal and industrial effluents as sources for water re-use.

Life Cycle Costing Assessment-Based Approach for Selection of Wastewater Treatment Units

There are several established and time tested technologies available for treatment of municipal wastewater. Each technology has its own merits and is in use globally for years depending on its suitability to satisfy a set of criteria. In the present work, the Life Cycle Cost Analysis (LCCA), also known as multi-criteria decision-analysis approach, has been used to subsequently develop a decision support tool. It assists efficiently in selection of the most suitable wastewater treatment technology for treating municipal wastewater. Quantitative weights from the LCCA are used to compare alternative systems with similar outcomes in addressing the system’s objective, having different cost structures, reliability and effluent quality. This paper focuses to evaluate suitability of wastewater treatment technologies in different situations. The generally adopted three technology options considered in the study are: (A) Trickling filter system (B) Waste stabilization pond (C) Activated sludge process. LCCA has been used to select a treatment unit for 12 MLD plant of municipal wastewater semi-urban locality. The waste stabilization pond technology has been found to have the lowest life time cost and cost effective option.

Developing a zero liquid discharge process for zeolitization of coal fly ash to synthetic NaP zeolite

Successful conversion of coal fly ash (CFA) to synthetic NaP zeolite with zero liquid discharge is reported in this article. The process eliminates the need for large amounts of water and the need for a huge wastewater treatment unit. The need for water, as a make-up stream, is only to compensate water losses during sampling and drying. Savings associated with minimizing make-up water and eliminating wastewater treatment unit can be substantial. Water and sodium hydroxide consumption is reduced by 90% and 50%, respectively. Furthermore, quality of the NaP zeolite (CFA-ZP) obtained is comparable to conventional method. The zeolitized product shows high crystallinity and leach resistance toward heavy metal and trace element content of the product. Leaching tests revealed that the concentrations of most of trace elements in leachate of CFA-ZP were less than threshold limit for landfill leachate and wastewater effluent for discharging into river and surface water.

Greywater Treatment with Simultaneous Generation of Energy Using Low-Cost Microbial Fuel Cells

Microbial fuel cells (MFCs) are an emerging type of biological wastewater treatment units with simultaneous power generation. The present study demonstrates an effective treatment of greywater and generation of electricity in a double-chambered MFC. This MFC was fabricated using cost-effective and easily available materials replacing expensive materials like Nafion membranes, graphite electrodes, etc. Experimental results showed a maximum open circuit voltage of 0.64 ± 0.04 V and 114 ± 1.41 mA current during the study period. The results further indicate a maximum power generation of 24.50 mW along with 307.69 mW/m² of power density; 34.62 mA/m² of current density, 1.33 W/m³ of volumetric power density, 0.15 A/m³ of volumetric current density and a power yield of 0.40 mW /kg of COD removal. The chemical oxygen demand (COD) removal efficiency was 77.6 %. The use of low-cost and easily available raw materials has brought down the total manufacturing cost of MFCs used in this study to less than USD 4.0. However, the performance of the MFCs used in the current study is comparable with other sophisticated MFCs built with expensive raw materials reported in the literature. This cost-effective MFC used in the present study might be an effective replacement of expensive MFCs for wastewater treatment at scaled-up levels. DOI: http://dx.doi.org/10.5755/j01.erem.71.3.11482

Forward osmosis membrane bioreactor for wastewater treatment with phosphorus recovery

A forward osmosis membrane bioreactor (OMBR) with a thin film composite membrane was seeded with flocculated sludge and aerobic granules to treat a synthetic wastewater with 1M NaCl as draw solution. The tested OMBR showed 96%, 43% and 100% removal of PO43−-P, NH4+-N, and total organic carbon. Salinity was accumulated in OMBR principally owing to membrane rejection and salt leakage from draw solution. At high salinity level membrane fouling could be induced. Intermittent withdrawal and replenishment of supernatant from OMBR maintained its operation stability, while phosphorus in withdrawn supernatant was recovered by pH adjustment. The OMBR enriched phosphorus concentration from 156mg/L in feed solution to 890–990mg/L. At pH 8.5 with 2.65–2.71g3M NaOH/g-P, 814–817mg-P/L was recovered in the form of sodium hydrogen phosphite hydrate. The OMBR is a volatile wastewater treatment unit with capability for enrichment and recovery of phosphorus at reduced chemical costs.

Biological treatment of high NH4+-N wastewater using an ammonia-tolerant photosynthetic bacteria strain (ISASWR2014)

Wastewater with high NH4+-N is difficult to treat by traditional methods. So in this paper, a wild strain of photosynthetic bacteria was used for high NH4+-N wastewater treatment together with biomass recovery. Isolation, identification, and characterization of the microorganism were carried out. The strain was inoculated to the biological wastewater treatment unit. The impacts of important factors were examined, including temperature, dissolved oxygen, and light intensity. Results showed that photosynthetic bacteria could effectively treat high NH4+-N wastewater. For wastewater with NH4+-N of 2300mg·L−1, COD/N=1.0, 98.3% of COD was removed, and cell concentration increased by 43 times. The optimal conditions for the strain's cell growth and wastewater treatment were 30°C, dissolved oxygen of 0.5–1.5mg·L−1 and a light intensity of 4000lx. Photosynthetic bacteria could bear a lower C/N ratio than bacteria in a traditional wastewater treatment process, but the NH4+-N removal was only 20%–40% because small molecule carbon source was used prior to NH4+-N. Also, the use of photosynthetic bacteria in chicken manure wastewater containing NH4+-N about 7000mg·L−1 proved that photosynthetic bacteria could remove NH4+-N in a real case, finally, 83.2% of NH4+-N was removed and 66.3% of COD was removed.

Do wastewater treatment plants act as a potential point source of microplastics? Preliminary study in the coastal Gulf of Finland, Baltic Sea.

This study on the removal of microplastics during different wastewater treatment unit processes was carried out at Viikinmäki wastewater treatment plant (WWTP). The amount of microplastics in the influent was high, but it decreased significantly during the treatment process. The major part of the fibres were removed already in primary sedimentation whereas synthetic particles settled mostly in secondary sedimentation. Biological filtration further improved the removal. A proportion of the microplastic load also passed the treatment and was found in the effluent, entering the receiving water body. After the treatment process, an average of 4.9 (±1.4) fibres and 8.6 (±2.5) particles were found per litre of wastewater. The total textile fibre concentration in the samples collected from the surface waters in the Helsinki archipelago varied between 0.01 and 0.65 fibres per litre, while the synthetic particle concentration varied between 0.5 and 9.4 particles per litre. The average fibre concentration was 25 times higher and the particle concentration was three times higher in the effluent compared to the receiving body of water. This indicates that WWTPs may operate as a route for microplastics entering the sea.

Application of CFD methods to an anaerobic digester: The case of Ontinyent WWTP, Valencia, Spain

In recent years, Computational Fluid Dynamics (CFD) methods have increasingly been used to characterize hydrodynamics and mass-transport in wastewater treatment units. Despite being a well-known and widely applied treatment method to stabilize sludge before final disposal, the hydrodynamics and mass transport in the anaerobic digester have been less studied than those of other treatment units. This paper presents the preliminary results of a 3D numerical study, investigating the characteristics of sludge flow inside the Ontinyent Wastewater Treatment Plant anaerobic digester (Valencia, Spain). An approach based upon the Reynolds Averaged Navier-Stokes (RANS) equation was applied, and closure was obtained using the classical standard k–ϵ model. In this particular case, a single-phase model was applied considering both Newtonian and Non Newtonian behavior for the sludge simulations. These single-phase preliminary results allowed the occurrence of dead zones to be identified as well as possible shortcuts inside the digester. The analysis was carried out considering the velocities and the flow patterns inside the digester as well as the sludge volume in the digester that had lower velocities than a determined settling velocity. The model was calibrated using available experimental pressure and temperature data. Finally, as well-mixed conditions are strongly desirable for effective anaerobic digestion, proposals to reduce the volume of dead zones are suggested and discussed.

Assessment of bioaerosol contamination (bacteria and fungi) in the largest urban wastewater treatment plant in the Middle East.

Bioaerosol concentration was measured in wastewater treatment units in south of Tehran, the largest wastewater treatment plant in the Middle East. Active sampling was carried out around four operational units and a point as background. The results showed that the aeration tank with an average of 1016 CFU/m(3) in winter and 1973 CFU/m(3) in summer had the greatest effect on emission of bacterial bioaerosols. In addition, primary treatment had the highest impact on fungal emission. Among the bacteria, Micrococcus spp. showed the widest emission in the winter, and Bacillus spp. was dominant in summer. Furthermore, fungi such as Penicillium spp. and Cladosporium spp. were the dominant types in the seasons. Overall, significant relationship was observed between meteorological parameters and the concentration of bacterial and fungal aerosols.

A novel application of genetic algorithm for synthesizing optimal water reuse network with multiple objectives

The current drive towards water conservation has compelled the process industries to seek various measures to minimize water. One such strategy is to design and synthesize an optimum water network that enables maximum reuse in between operations. Such optimization has been known to be challenging due to the presence of nonlinearities in the formulation that makes it difficult to solve using the standard deterministic techniques. Moreover, most of these techniques have focused on solving single objective problem involving freshwater usage while other decision factors such as treatment costs and network topologies are generally not accounted for as they would introduce extra complexities to the problem. In this paper, we propose to address optimal water reuse network as a multi-objective optimization problem—our strategy is to apply a well-known genetic algorithm (NSGA-II) for single- or multi-objective optimization of water reuse network synthesis in a total (integrated) setting. First, a superstructure entailing all reuse opportunities between the water-using processes and wastewater treatment units is formulated. Next, decision variables in the form of various stream flows are encoded as the initial population chromosomes and then subjected to a set of genetic operators (selection, mutation, and crossover) to generate the offspring chromosomes. Coupled with these operators is an elitism strategy to improve the convergence and spread of the solutions. A key benefit of this approach is that it can be equally applied for both single objective and multi-objective cases in a robust manner. To demonstrate the efficacy of the approach, four single-objective case studies are solved with the results compared with the reported global optima. Thereafter, two multi-objective case studies are solved to generate the complete Pareto set. The key advantage of the proposed approach lies in its ability to solve complex optimization problem without resorting to simplifying heuristics and optimization strategies that are characteristics of the literature approaches.

Optimal Wastewater Treatment Design by Using Genetic Algorithm

Integrated advanced wastewater treatment provides important fundamental solutions to problems associated with water scarcity prevailing in arid and semi-arid climatic regions.This was accomplished through treated water with specific specification and characteristics suitable to be used for agricultural, domestic, and industrial purposes. This study is concerned with the use of genetic algorithm procedure for the optimum design of integrated advance wastewater treatment units, with their various types and characteristics. The aim of optimum wastewater treatment units design is to attain optimum values of certain pre-defined objective function. The objective function is to satisfy certain constraints and achieve minimum capital, maintenance, and operation costs.Chemical clarification treatment unit was used in this study.This study includes development of computer program for advances wastewater treatment plants design adopting genetic algorithm. The program was developed using Matlab software. The results obtained from this study include the finding of optimum design criteria for advanced wastewater treatment plants. The obtained design criteria are satisfying the required water quality with minimum treatment cost.

Wastewater Treatment Process Study for Used Diaper Recycling

ABSTRACT This study aims to suggest wastewat er treatment options for diaper recycling by identifying characteristic analysis of wastewater from diaper recycling proces s and efficiency evaluation of wastewater treatment units. The wastewater characteristic analysis showed that the concentration of organic pollutants and ion-ic materials were very hi gh comparing to seawater. Through the in vestigation of similar wastewater treat-ment, six treatment units were identified to reduce pollutants. It is found UF(ultra-filtration), DAF(dis-solved air flotation), fenton oxidation, electro-coagulation and chemical-coagulation are effective in re-ducing organic pollutants while membrane system and ion exchanger are effective in reducing ionic materials. Even though the target of water quality sh ould be secured in terms of managing organic pollu-tants level, the application of treatment unit for reducing ionic material needs lots of considerations. This result suggests that reuse of pulping wastewater after controlling organic pollutants is better than direct discharge of pulping wastewater. To select the appropriate wastewater treatment unit, an economic anal-ysis about operation condition, wastewater flow, cost, efficiency should be considered.