Anaerobic Wastewater Treatment Process Research Articles

Using the kriging method based on cross-validation stepwise variable selection to optimize anaerobic wastewater treatment process

Using the kriging method based on cross-validation stepwise variable selection to optimize anaerobic wastewater treatment process

Bioponic systems with biochar: Insights into nutrient recovery, heavy metal reduction, and microbial interactions in digestate-based bioponics

Bioponics is a nutrient-recovery technology that transforms nutrient-rich organic waste into plant biomass/bioproducts. Integrating biochar with digestate from anaerobic wastewater treatment process can improve resource recovery while mitigating heavy metal contamination. The overarching goal of this study was to investigate the application of biochar in digestate-based bioponics, focusing on its efficacy in nutrient recovery and heavy metal removal, while also exploring the microbial community dynamics. In this study, biochar was applied at 50 % w/w with 500 g dry weight of digestate during two 28-day crop cycles (uncontrolled pH and pH 5.5) using white stem pak choi (Brassica rapa var. chinensis) as a model crop. The results showed that the digestate provided sufficient phosphorus and nitrogen, supporting plant growth. Biochar amendment improved plant yield and phosphate solubilization and reduced nitrogen loss, especially at the pH 5.5. Furthermore, biochar reduced the heavy metal accumulation in plants, while concentrating these metals in the residual sludge. However, owing to potential non-carcinogenic and carcinogenic health risks, it is still not recommended to directly consume plants cultivated in digestate-based bioponic systems. Additionally, biochar amendment exhibited pronounced impact on the microbial community, promoting microbes responsible for nutrient solubilization and cycling (e.g., Tetrasphaera, Herpetosiphon, Hyphomicrobium, and Pseudorhodoplanes) and heavy metal stabilization (e.g., Leptolinea, Fonticella, Romboutsia, and Desulfurispora) in both the residual sludge and plants. Overall, the addition of biochar enhanced the microbial community and facilitated the metal stabilization and the cycling of nutrients within both residual sludge and root systems, thereby improving the overall efficiency of the bioponics.

Innovations for the Treatment of Effluents in the Food Industry

During the processing phases of the food business, a large amount of water is used, resulting in a large volume of effluents. Raw materials, sanitary water for food processing, transportation, cooking, dissolving, auxiliary water, cooling, cleaning, and so on are all utilized extensively in the business. Traditional anaerobic or aerobic biological wastewater treatment processes can be employed to handle organic compounds found in food sector effluent. However, some hazardous chemicals to a microbial population may be present in the effluent due to varied consumption. The effluent may contain significant levels of suspended particles, nitrogen in various chemical forms, lipids, oils, phosphorus, chlorides, and high organic content. There are traditional and well-established methods for treating effluents in the food industry, such as the coagulation-flocculation process, electrochemical processes, and biological processes, which have proven to be quite effective when used as treatment methods in a variety of industries; however, such methods have limitations. Innovative techniques, such as microbial fuel cells (MFCs), microalgae, water ultrafiltration, nanofiltration, and membrane technologies, can replace or complement traditional methods in the future. The treatment method chosen will be determined by the industry's and its wastewater's characteristics.

Novel Use of a Ferric Salt to Enhance Mainstream Nitrogen Removal from Anaerobically Pretreated Wastewater.

This study aims to demonstrate a new technology roadmap to support the ongoing paradigm shift in wastewater management from pollutant removal to resource recovery. This is achieved by developing a novel use of an iron salt (i.e., FeCl3) in an integrated anaerobic wastewater treatment and mainstream anammox process. FeCl3 was chosen to be dosed in a proposed sidestream unit rather than in a primary settler or a mainstream reactor. This causes acidification of returned activated sludge and enables stable suppression of nitrite-oxidizing bacterial activity and excess sludge reduction. A laboratory-scale system, which comprised an anaerobic baffled reactor, a continuous-flow anoxic-aerobic (A/O) reactor, and a secondary settler, was designed to treat real domestic wastewater, with the performance of the system comprehensively monitored under a steady-state condition. The experimental assessments showed that the system had good effluent quality, with total nitrogen and phosphorus concentrations of 12.6 ± 1.3 mg N/L and 0.34 ± 0.05 mg P/L, respectively. It efficiently retained phosphorus in excess sludge (0.18 ± 0.03 g P/g dry sludge), suggesting its potential for further recovery. About half of influent organic carbon was recovered in the form of bioenergy (i.e., methane). This together with low energy consumption revealed that the system could produce a net energy of about 0.11 kWh/m3-wastewater, assessed by an energy balance analysis.

Impact of electrochemically generated iron on the performance of an anaerobic wastewater treatment process

Anaerobic treatment of domestic wastewater has the advantages of lower biomass yield, lower energy demand and higher energy recover over the conventional aerobic treatment process. However, the anaerobic process has the inherent issues of excessive phosphate and sulfide in effluent and superfluous H2S and CO2 in biogas. An electrochemical method allowing for in-situ generation of Fe2+ in the anode and hydroxide ion (OH−) and H2 in the cathode was proposed to overcome the challenges simultaneously. The effect of electrochemically generated iron (e‑iron) on the performance of anaerobic wastewater treatment process was explored with four different dosages in this work. The results showed that compared to control, the experimental system displayed an increase of 13.4–28.4 % in COD removal efficiency, 12.0–21.3 % in CH4 production rate, 79.8–98.5 % in dissolved sulfide reduction, 26.0–96.0 % in phosphate removal efficiency, depending on the e‑iron dosage between 40 and 200 mg Fe/L. Dosing of the e‑iron significantly upgraded the quality of produced biogas, showing a much lower CO2 and H2S contents in biogas in experimental reactor than that in control reactor. The results thus demonstrated that e‑iron can significantly improve the performance of anaerobic wastewater treatment process, bringing multiple benefits with the increase of its dosage regarding effluent and biogas quality.

An Artificial Neural Network for Simulation of an Upflow Anaerobic Filter Wastewater Treatment Process

The purpose of this work was to develop a problem-solving approach and a simulation tool that is useful for the specification of wastewater treatment process equipment design parameters. The proposition of using an artificial neural network (ANN) numerical model for supervised learning of a dataset and then for process simulation on a new dataset was investigated. The effectiveness of the approach was assessed by evaluating the capacity of the model to distinguish differences in the equipment design parameters. To demonstrate the approach, a mock dataset was derived from experimentally acquired data and physical effects reported in the literature. The mock dataset comprised the influent flow rate, the bed packing material dimension, the type of packing material and the packed bed height-to-diameter ratio as predictors of the calorific value reduction. The multilayer perceptron (MLP) ANN was compared to a polynomial model. The validation test results show that the MLP model has four hidden layers, each having 256 units (nodes), accurately predicts calorific value reduction. When the model was fed previously unseen test data, the root-mean-square error (RMSE) of the predicted responses was 0.101 and the coefficient of determination (R2) was 0.66. The results of simulation of all 125 possible combinations of the 3 mechanical parameters and identical influent wastewater flow profiles were ranked according to total calorific value reduction. A t-test of the difference between the mean calorific value reduction of the two highest ranked experiments showed that the means are significantly different (p-value = 0.011). Thus, the model has the capacity to distinguish differences in the equipment design parameters. Consequently, the values of the three mechanical feature parameters from the highest ranked simulated experiment are recommended for use in the design of the industrial scale upflow anaerobic filter (UAF) for wastewater treatment.

Principles, Advances, and Perspectives of Anaerobic Digestion of Lipids.

Several problems associated with the presence of lipids in wastewater treatment plants are usually overcome by removing them ahead of the biological treatment. However, because of their high energy content, waste lipids are interesting yet challenging pollutants in anaerobic wastewater treatment and codigestion processes. The maximal amount of waste lipids that can be sustainably accommodated, and effectively converted to methane in anaerobic reactors, is limited by several problems including adsorption, sludge flotation, washout, and inhibition. These difficulties can be circumvented by appropriate feeding, mixing, and solids separation strategies, provided by suitable reactor technology and operation. In recent years, membrane bioreactors and flotation-based bioreactors have been developed to treat lipid-rich wastewater. In parallel, the increasing knowledge on the diversity of complex microbial communities in anaerobic sludge, and on interspecies microbial interactions, contributed to extend the knowledge and to understand more precisely the limits and constraints influencing the anaerobic biodegradation of lipids in anaerobic reactors. This critical review discusses the most important principles underpinning the degradation process and recent key discoveries and outlines the current knowledge coupling fundamental and applied aspects. A critical assessment of knowledge gaps in the field is also presented by integrating sectorial perspectives of academic researchers and of prominent developers of anaerobic technology.

Modernization of Anaerobic Bioreactor for Waste Water Purification Plant

Analysis of literature sources suggests that the use of anaerobic treatment methods is especially effective for high concentrations of contaminants in wastewater, as well as for large volumes of water supplied for treatment, which is typical for industrial wastewater. In biotechnological production and food industry, waste water has a high level of pollution with organic compounds, it is advisable to use anaerobic treatment methods. Anaerobic wastewater treatment processes are characterized by low energy consumption and the ability to recover energy through the combustion of methane. To ensure the required temperature regime for the operation of the bioreactor, a new design of the heat exchange device of the anaerobic bioreactor with immobilized microorganisms has been developed. This design of the bioreactor can provide the required degree of wastewater purification at significantly lower costs for construction, operation, and material and energy resources. For clarity, the design features were designed bioreactor with a plane load of bundled software SOLIDWORKS and a mathematical model of the processes of anaerobic wastewater treatment.

Robust regulation of an anaerobic wastewater treatment model

This paper studies the dynamics of a nonlinear control system, modelling an anaerobic wastewater treatment process. Under suitable assumption we regulate the biological oxygen demand so that its values fall between prescribed bounds. Since the biological and the chemical oxygen demand are strongly related, this allows us to regulate the pollution concentration according to existing ecological norms. The regulation is done in the following manner: We fix bounds for the values of the control function (the dilution rate) and show that the values of the biological oxygen demand of the corresponding dynamics tend to a prescribed interval as time tends to infinity. We also present a variety of numerical simulations using randomly chosen admissible controls in order to illustrate the robustness of the obtained results.

Development of UASB–DHS System for Anaerobically-Treated Tofu Processing Wastewater Treatment under Ambient Temperature

Tofu is widely processed in East and Southeast Asian countries. During the production, highly polluted wastewater is discharged. This wastewater is commonly treated using a high-rate anaerobic wastewater treatment process; however, several organic compounds and nitrogen remain in the anaerobic effluent. The aim of this study was to develop a combined upflow anaerobic sludge blanket (UASB) and downflow hanging sponge (DHS) biosystem that that serves as a post-treatment for an expanded granular sludge blanket reactor used for treating tofu-processing wastewater in Japan for 699 days. The UASB reactor played a role in treating of COD, with 58 ± 16% and 74 ± 20% of total COD and soluble COD removed anaerobically. Besides, methane was recovered from removed soluble COD were 63 ± 28% and 87 ± 64% at winter and summer. Meanwhile, the DHS reactor showed its potential in treatment of BOD and TSS. The final effluents were recorded as 67 ± 38 mg·L-1, 50 ± 26 mg·L-1, and 22 ± 16 mg·L-1 of total COD, BOD and total suspended solids, respectively. This indicates that the proposed UASB-DHS system has proven its suitability as post-treatment system for anaerobically treated tofu-processing wastewater

Functional Interrelationships of Microorganisms in Iron-Based Anaerobic Wastewater Treatment.

This study explicated the functional activities of microorganisms and their interrelationships under four previously reported iron reducing conditions to identify critical factors that governed the performance of these novel iron-dosed anaerobic biological wastewater treatment processes. Various iron-reducing bacteria (FeRB) and sulfate reducing bacteria (SRB) were identified as the predominant species that concurrently facilitated organics oxidation and the main contributors to removal of organics. The high organic contents of wastewater provided sufficient electron donors for active growth of both FeRB and SRB. In addition to the organic content, Fe (III) and sulfate concentrations (expressed by Fe/S ratio) were found to play a significant role in regulating the microbial abundance and functional activities. Various fermentative bacteria contributed to this FeRB-SRB synergy by fermenting larger organic compounds to smaller compounds, which were subsequently used by FeRB and SRB. Feammox (ferric reduction coupled to ammonium oxidation) bacterium was identified in the bioreactor fed with wastewater containing ammonium. Organic substrate level was a critical factor that regulated the competitive relationship between heterotrophic FeRB and Feammox bacteria. There were evidences that suggested a synergistic relationship between FeRB and nitrogen-fixing bacteria (NFB), where ferric iron and organics concentrations both promoted microbial activities of FeRB and NFB. A concept model was developed to illustrate the identified functional interrelationships and their governing factors for further development of the iron-based wastewater treatment systems.

Moving average convergence and divergence indexes based online intelligent expert diagnosis system for anaerobic wastewater treatment process

Anaerobic wastewater treatment process is efficient but unstable due to various disturbances, such as refractory organics and influent organic overloading. Therefore, sensitive and accurate status diagnosis is important for reasonable control to improve the stability of anaerobic process. In this study, an online intelligent expert diagnosis system for anaerobic process was established based on moving average convergence and divergence (MACD) indexes of gas- and liquid-phase parameters, combined with online monitoring system and expert diagnosis database. The effect of this diagnosis system was verified through refractory organics and organic overloading shock experiments. Results showed that this diagnosis system could make rapid, accurate and comprehensive diagnosis, predictions and early-warning. MACD algorithm could enhance pattern recognition capacity of status parameters, overcome the lagging of anaerobic process and filter irregular noisy fluctuations of status parameters. MACD index of H2 partial pressure is suitable as sensitive early-warning indicator in the initial shock stage.

WASTEWATER PURIFICATION FROM ANTIBIOTICS WITH SIMULTANIOUS BIOGAS PRODUCTION

The possibility of biogas obtaining in a pharmaceutical plant anaerobic wastewater treatment process, which contains antibiotics of different classes (tetracycline, norfloxacin, cephalosporin, penicillin) has been studied. The enzymatic process was conducted in the mesophilic regime (37 ± 1 ° C) using free-floating and granulated anaerobic sludge. As granulation centers, talc-based sorbents were used. It was shown that wastewater treatment efficiency depends on the inoculum type, wastewater component composition and antibiotics content. With the use of granulated anaerobic sludge, during distillery wastewater treatment with norfloxacin content 10 mg / dm3 and tetracycline 191 cm3 / g of wastewater the biogas yield reaches 254 cm3 / g of wastewater, and methane content reaches 70%.

Wetting- and fouling-resistant hollow fiber membranes for dissolved methane recovery from anaerobic wastewater treatment effluents

Anaerobic wastewater treatment processes are becoming increasingly widespread due to their advantages in sludge management and net energy consumption. One major reason behind the energy benefit of the mainstream anaerobic processes is methane (CH4) production. Nevertheless, over one-third of the produced CH4 typically remains in effluent streams in dissolved form. To recover the dissolved CH4 (dCH4) from anaerobic effluents, the membrane contactor (MC) process enabled by porous membranes offers a promising way. However, membrane wetting and fouling issues hinder the practical implementation of the concept. Here we report a wetting- and fouling-resistant hollow fiber membrane that can operate with realistic anaerobic effluents. Coating of a highly porous (~85%) hollow fiber support with a conformal layer of polydimethylsiloxane (PDMS) provides resistance to wetting, but fouling persists. To tackle the fouling issue, we post-treated the uncured PDMS-coatings with PDMS-based amphiphilic copolymers with short (147 Da) or long (~1570 Da) side chains. Both types of post-treated membranes exhibited an improved performance when tested against effluent samples taken not only from an anaerobic membrane bioreactor but also from an upflow anaerobic sludge blanket (UASB) reactor. The membrane treated with the short-side-chain copolymer could sustain 7 days of continuous operation with UASB effluent with a performance loss of only ~10%. We observed that the fouling layers were much richer in proteins rather than subtances similar to humic and fulvic acids and microbial byproducts. Besides, we calculated that our wetting/fouling-resistant membranes provide a net energy benefit for the MC process (when the recovered CH4 is retrofitted to the process as fuel). Thus, our results suggest that the MC-based dCH4 recovery process is a viable alternative for industrial practices in case the demonstrated custom-designed membranes are employed.

A high-throughput assay to quantify protein hydrolysis in aerobic and anaerobic wastewater treatment processes.

Proteins, an important fraction of the organic matter in wastewater, typically enter a treatment facility as high molecular weight components. These components are degraded by extracellular protein hydrolytic enzymes, denoted as proteases. Adequate protein hydrolysis monitoring is crucial, since protein hydrolysis is often a rate-limiting step in wastewater treatment. However, current monitoring tools lack a high sample throughput and reliable quantification. Here, we present an improved assay for high-throughput protein hydrolysis rate measurements in wastewater treatment applications. A BODIPY FL casein model substrate was implemented in a microplate format for continuous fluorescent quantification. Case studies on a conventional and a high-rate aerobic municipal wastewater treatment plant and a lab-scale, two-stage, anaerobic reactor provided proof-of-concept. The assay presented in this study can help to obtain monitoring-based process insights, which will in turn allow improving biological performance of wastewater treatment installations in the future. KEY POINTS: • Protein hydrolysis is a crucial step in biological wastewater treatment. • Quantification of the protein hydrolysis rate enables in-depth process knowledge. • BODIPY FL casein is a suitable model substrate for a protein hydrolysis assay. • High sample throughput was obtained with fluorescent hydrolysis quantification. Graphical abstract.

Recovery of dissolved methane from anaerobically treated food waste leachate using solvent-based membrane contactor

The difficulty of dissolved methane recovery remains a major hurdle for mainstream anaerobic wastewater treatment processes. We recently proposed solvent-based membrane contactor (SMC) for high (>90%) methane recovery over a wide temperature range and net-energy production. Here, we investigate the methane recovery efficacy of the SMC process by using an AnMBR effluent from treating food waste leachate. We observed almost identical methane transfer kinetics to the process employing foulant-free methane-saturated feed solutions, with >92% methane recoveries, showing that organic foulants have insignificant impacts on the methane transport in the SMC. We then performed two different membrane contactor experiments: direct-contact membrane-distillation (DCMD, with transmembrane water vapor flow) and SMC (no water vapor flow). From the negligible fouling observed in the SMC experiment, opposite to the DCMD, we elucidate that the absence of water vapor flow renders the SMC process intrinsically robust to membrane fouling. With the low fouling propensity of the SMC process under highly fouling environments, our study highlights the feasibility of SMC processes to enhance the energy production in mainstream anaerobic wastewater treatment processes.

Design and evaluation of degassed anaerobic membrane biofilm reactors for improved methane recovery

Anaerobic treatment of domestic wastewater (DWW) produces dissolved methane that needs to be recovered for use as an energy product. Membrane-based recovery systems have been reported in the literature but are often limited by fouling. The objective of this study was to develop a methane producing biofilm on the shell side surface a membrane to allow for immediate recovery of methane as it was produced, negating mass transfer resistance caused by fouling. Between 89 and 96% of total methane produced was recovered via in-situ degassing without the need for fouling control or cleaning throughout 72 weeks of operation. High methane recovery efficiencies led to predictions of net positive energy yield in one reactor and a 32–61% reduction in energy demand in the others compared to the control. This research demonstrates the feasibility and usefulness of combining attached growth anaerobic wastewater treatment processes with hollow fiber membrane methane recovery systems for improved operation.

Online prediction of effluent COD in the anaerobic wastewater treatment system based on PCA-LSSVM algorithm.

Since anaerobic wastewater treatment is a nonlinear and complex biochemical process, reasonable monitoring and control are needed to keep it operating stably and efficiently. In this paper, a least-square support-vector machine (LS-SVM) was employed to construct models for the prediction of effluent chemical oxygen demand (COD) in an anaerobic wastewater treatment system. The result revealed that the performance of the steady-state model based on LS-SVM for predicting effluent COD was acceptable, with the maximum relative error (RE) of 11.45%, the mean average percentage error (MAPE) of 0.79% and the root mean square error (RMSE) of 3.08 when training, and the performance fell slightly when testing. Even though, the correlation coefficient value (R) between the predicted value and the actual value of 0.9752 could be achieved, which means this model can predict the variation of effluent COD in general. The dynamic-state models under three kinds of shock loads, which were concentration, hydraulic, and bicarbonate buffer absent, showed good forecasting performance, the correlation coefficient values (R) all excelled 0.99. Among these three shocks, the dynamic LS-SVM model under bicarbonate buffer absent shock achieved the optimal performance and followed by the dynamic-state model under hydraulic shock. This paper provides a meaningful reference to improve the monitoring level of the anaerobic wastewater treatment process.

Dissolved Methane Harvesting Using Omniphobic Membranes for Anaerobically Treated Wastewaters

Dissolved biomethane in anaerobic effluents has long been a hurdle for energy harvesting through anaerobic wastewater treatment processes. Here, we present a novel membrane process for dissolved methane recovery through the normal range of domestic wastewater temperatures by utilizing an omniphobic (nonwetting) microporous membrane. In a process driven by a solubility gradient, dissolved methane is extracted from a methane-rich aqueous solution (feed), transported across the omniphobic membrane, and absorbed into a nonpolar organic solvent (draw) that has a high solubility for methane. We fabricated the omniphobic membrane by coating a microporous polymeric membrane with silica nanoparticles, followed by surface fluorination. Using the omniphobic membrane, we demonstrate that nearly ≥90% of dissolved methane is recovered from methane-saturated feedwater at 15, 25, and 35 °C, simulating anaerobic effluents produced in the psychrophilic to mesophilic temperature range, while negligible transport of water is...

Greenhouse gas emission estimation for a UASB reactor in a dairy wastewater treatment plant

Greenhouse gases (GHGs) emissions have been increasing, recently. One of the greenhouse gas emission resources is the anaerobic wastewater treatment process. The up flow anaerobic sludge bed (UASB) reactor is the anaerobic treatment unit located in a dairy wastewater treatment plant (WWTP) in Turkey. Greenhouse gases (GHGs) emission emits from the anaerobic reactor due to the biogas generation. In this study, the on-site greenhouse gas emissions from the anaerobic reactor with and without biogas recovery were estimated from biogas amount and content using a developed model based on IPCC approach. Then, the off-site GHGs emissions were estimated from electricity consumption and chemical use. The biogas recovery reduced the greenhouse gas emissions. The highest reduction of the on-site GHGs emissions was 97%. Chemical use was the major source of the off-site GHGs emissions in this study. The main emission resource was chemical consumption for a UASB reactor located in a dairy WWTP.