Conventional Activated Sludge Process Research Articles

Removal and prediction of chemicals in anaerobic–anoxic–aerobic wastewater treatment system: Case study on organophosphates

Distribution and removal of chemicals in wastewater treatment plants (WWTPs) have mainly relied on mathematical models. Existing exposure assessment models such as SimpleTreat, STPWIN are based on conventional activated sludge processes. There is an urgent need to develop an A2/O-based WWTPs exposure assessment model. Organophosphates (OPEs) have different physical and chemical properties and potential environmental risks. The fate and biodegradation kinetics of three types of OPEs, including alkyl OPEs, chlorinated OPEs and triphenyl ester OPEs, were studied in a laboratory-scale anaerobic/anoxic/aerobic (A2/O) sewage treatment system and batch reactors. The three types of OPEs had different anaerobic, anoxic, and aerobic removal characteristics. A compensation mechanism was found between anaerobic and anoxic/aerobic removal. When the hydraulic retention time decreased from 82 to 20.5 h, the removal efficiencies in the anaerobic unit decreased, while those in the anoxic unit increased; as a result, the total removal efficiencies remained high (>80 %) for all OPEs except triphenyl phosphate (65.5%–75.1 %). The concept of effective sludge concentration (MLSSeff) was proposed to illustrate the compensation mechanism and calibrate the second-order kinetic equation for predicting pollutant removal in the A2/O system: MLSSeff = ken × MLSS, where ken is a constant related to the influent total organic carbon content (TOC). The influent TOC contents of the anoxic and aerobic units affected the value of MLSSeff and OPEs removal. The results are of great significance for assessing OPEs exposure and predicting exposure to emerging micropollutants in sewage treatment systems.

Study on the compatibility of a treated effluent from automobile industry with conventional municipal activated sludge process

AbstractThe on-site-treated effluent from an automobile manufacturing company is discharged into the public sewage system for further treatment. However, the upgrade of the treatment plant to reduce the effluent pollutant load led to the discharge limit for phenols being occasionally exceeded. The concern of the water authority prompted a study to investigate whether the toxicity of phenols could affect the performance of the receiving municipal wastewater treatment plant. To this end, mixtures of the industrial effluent and synthetic municipal wastewater were tested in a laboratory-scale activated sludge system. The bioreactor was fed with increasing ratios of the industrial wastewater in the combined influent (from 10 to 50%) over 7 months. No significant differences were observed in the system performance fed only with the synthetic wastewater (during the acclimation stage) or with the industrial wastewater. The bioreactor achieved average removal efficiencies of 70% for phenols even when half of the combined influent was the industrial wastewater. Bearing in mind the question of phenols, an important drawback was the high uncertainty in their determination by the conventional phenol index method due to the matrix effect. To overcome this a spectrophotometric procedure based on the serial dilutions of each pair of influent and effluent samples has been developed. Although strong microbial selection was observed by the changing bioreactor environment, the industrial effluent was found to be fully compatible with further treatment by conventional activated sludge process.

Biological wastewater treatment: a comprehensive sustainability analysis using life cycle assessment.

The research conducts a life cycle assessment (LCA) on wastewater treatment (WWT) methods-membrane bioreactor (MBR), soil biotechnology (SBT), and bio-electrochemical constructed wetlands (BCW)-in comparison with the conventional activated sludge process (ASP). Employing SimaPro v9.5 with a cradle-to-gate system boundary, the analysis utilizes the IMPACT 2002 + method, employing per cubic meter of treated wastewater as the functional unit. The analysis shows that SBT exhibits the lowest environmental impacts among the considered WWT methods. The global warming potential was 0.0996 kg CO2 eq. for SBT, 1.33 kg CO2 eq. for MBR, 0.131 kg CO2 eq. for BCW, and 0.544 kg CO2 eq. for ASP. BCW demonstrates a 75.91% decrease, while MBR exhibits a 144.48% increase compared to ASP. Notably, electricity consumption emerges as the primary contributor to environmental impact in MBR and ASP. The resource impact category varies with a 138.15% increase in MBR and an 83.41% decrease in SBT compared to ASP. Additionally, the research indicates that the high human health impact observed in MBR results mainly from increased carcinogens (0.00176 kg C2H3Cl eq.), non-carcinogens (0.01 kg C2H3Cl eq.), and ionizing radiation (3.34 Bq C-14 eq.). The findings underscore the importance of considering treatment efficiency and broader environmental implications in selecting WWT methods. As the world emphasizes sustainability, such LCA studies provide valuable insights for making informed decisions in wastewater management.

Micropollutant biotransformation under different redox conditions in PhoRedox conventional activated sludge systems

The ecotoxicological safety of the water bodies relies on the reduction of micropollutant emissions from wastewater treatment plants (WWTP). The ecotoxicological safety of the water bodies relies on the reduction of micropollutant emissions from wastewater treatment plants (WWTP). Quantification of micropollutant removal at full-scale WWTP is scarce. To our knowledge, the anaerobic conversion rates determined at conventional activated sludge processes are, so far, scarcely available in the literature for most of the micropollutants. In this research, we quantified the biotransformation rate constants and the removal efficiencies of 16 micropollutants (4,5-methylbenzotriazole, azithromycin, benzotriazole, candesartan, carbamazepine, clarithromycin, diclofenac, gabapentin, hydrochlorothiazide, irbesartan, metoprolol, propranolol, sotalol, sulfamethoxazole, trimethoprim, and venlafaxine), under aerobic, anoxic, and anaerobic redox conditions; using as inoculum wastewater and biomass from a full-scale conventional activated sludge (CAS) system in the Netherlands. Clarithromycin was the compound that exhibited the highest aerobic (76%) and anaerobic (78%) removal efficiencies, while gabapentin showed the highest removal under anoxic conditions (91%). A preference for cometabolic biotransformation of the targeted micropollutants was observed. The highest biotransformation rate constants obtained were: at aerobic conditions clarithromycin with 1.46L.gSS-1.d-1; at anoxic conditions, gabapentin with 2.36L.gSS-1.d-1; and at anaerobic redox conditions clarithromycin with 1.87L.gSS-1.d-1. The obtained results of biotransformation rates will allow further modelling of micropollutant removal in CAS systems, under various redox conditions. These biotransformation rates can be added to extended ASM models to predict effluent concentration and optimize targeted advanced oxidation processes allowing savings in the operational costs and increasing the process viability.

Wastewater surveillance of antibiotic resistance and class 1 integron-integrase genes: potential impact of wastewater characteristics on genes profile

Antibiotic resistance (AR) is a major global health concern, but current surveillance efforts primarily focus on healthcare settings, leaving a lack of understanding about AR across all sectors of the One Health approach. To bridge this gap, wastewater surveillance provides a cost-effective and efficient method for monitoring AR within a population. In this study, we implemented a surveillance program by monitoring the wastewater effluent from two large-scale municipal treatment plants situated in Isfahan, a central region of Iran. These treatment plants covered distinct catchment regions and served a combined population about two million of residents. Furthermore, the effect of physicochemical and microbial characteristics of wastewater effluent including biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), temperature, total coliforms and Escherichia coli concentration on the abundance of ARGs (blaCTX-M, tetW, sul1, cmlA, and ermB) and class 1 integron-integrase gene (intI1) were investigated. Sul1 and blaCTX-M were the most and least abundant ARGs in the two WWTPs, respectively. Principal Component Analysis showed that in both of the WWTPs all ARGs and intI1 gene abundance were positively correlated with effluent temperature, but all other effluent characteristics (BOD, COD, TSS, total coliforms and E. coli) showed no significant correlation with ARGs abundance. Temperature could affect the performance of conventional activated sludge process, which in turn could affect the abundance of ARGs. The results of this study suggest that other factors than BOD, COD and TSS may affect the ARGs abundance. The predicted AR could lead to development of effective interventions and policies to combat AR in the clinical settings. However, further research is needed to determine the relationship between the AR in wastewater and clinical settings as well as the effect of other influential factors on ARGs abundance.

MBR and GAC filtration followed by UV disinfection – implications for wastewater reuse at full scale

Abstract Influences of upstream wastewater treatment on the process combination of granular activated carbon (GAC) and ultraviolet (UV) disinfection were studied and the implications of this for wastewater reuse were assessed. GAC is an efficient chemical barrier but contributes little to the removal of indicator bacteria, and generally increases total bacteria concentrations, necessitating disinfection with UV radiation, for example, to ensure the safe reuse of wastewater. The efficiency of UV disinfection is impacted by factors such as particle concentration and UV absorbance of the water and is thus affected by upstream treatment processes. A full-scale wastewater treatment plant with a membrane bioreactor (MBR) followed by GAC filtration was compared to a treatment plant with a conventional activated sludge process and sand filtration, followed by GAC filtration. The removal of indicator bacteria was higher by the GAC filter that was preceded by an MBR. A UV fluence of 400 J/m2 was sufficient to reach irrigation water quality for both process combinations and to meet the criteria for microbial drinking water quality in the MBR + GAC effluent. One sample was selected for chemical analysis, comprising approximately 100 parameters, demonstrating that the MBR + GAC + UV (400 J/m2) effluent met all drinking water criteria except for nitrate levels.

Optimized process intensification through dynamic performance simulation and evaluation of treatment alternatives for a wastewater treatment plant in Toronto

In this study, a comprehensive plant-wide model of the North Toronto Treatment Plant (NTTP) was developed, focusing on improving operational efficiency and capacity utilization. NTTP, with a rated capacity of 45 MLD, is currently operating at about 18 MLD with treatment processes including physical units (incorporating four primary settling tanks), chemical precipitation (for phosphorus removal using ferrous chloride), and biological processes (utilizing eight plug-flow conventional activated sludge (CAS) aeration tanks), and two sets of final clarifiers. Utilizing Biowin 6.2, the study constructed and calibrated a mechanistic model based on historical plant records and extensive sampling campaign data gathered from July to August 2022. The performance of various process configurations under different operational and seasonal conditions was evaluated. It was observed that the Ludzack-Ettinger (L-E) configuration demonstrated enhanced performance in terms of Environmental Compliance Approval (ECA) objectives and cost-efficiency compared to the CAS process. However, the L-E configuration posed challenges related to the final clarifier loading. The State Point Analysis (SPA) conducted within the study emphasized the effectiveness of the Membrane Aerated Bioreactor (MABR) in producing high-quality effluent, while also reducing the burden on the final clarifiers. This research provides a foundation for potential upgrades to NTTP, leveraging existing infrastructure to approach its full rated capacity while maintaining adherence to current ECA objectives.

A novel approach for purifying food waste anaerobic digestate through bio-conditioning dewatering followed by activated sludge process: A case study

Although anaerobic digestion is the mainstream technology for treating food waste (FW), the high pollutant concentration in the resultant food waste anaerobic digestate (FWAD) often poses challenges for the subsequent biochemical treatment such as activated sludge process. In this study, taking a typical FW treatment plant as an example, we analyzed the reasons behind the difficulties in treating FWAD and tested a novel process called as bio-conditioning dewatering followed by activated sludge process (BDAS) to purify FWAD. Results showed that high concentrations of suspended solids (SS) (16439 ± 475 mg/L), chemical oxygen demand (COD) (24642 ± 1301 mg/L), and ammonium nitrogen (NH4+-N) (2641 ± 52 mg/L) were main factors affecting the purification efficiency of FWAD by the conventional activated sludge process. By implementing bio-conditioning dewatering for solid-liquid separation, near 100% of SS and total phosphorus (TP), 90% of COD, 38% of total nitrogen (TN), and 37% of NH4+-N in the digestate could be effectively removed or recovered, consequently generating the transparent filtrate with relatively low pollution load and dry sludge cake (<60% of moisture content). Furthermore, after ammonia stripping and biochemical treatment, the effluent met the relevant discharge standards regulated by China, with the concentrations of COD, TN, NH4+-N, and TP ranging from 151 to 405, 10–56, 0.9–31, and 0.4–0.8 mg/L, respectively. This proposed BDAS approach exhibited stable performance and low operating costs, offering a promising solution to purify FWAD in practical engineering and simultaneously realize resource recovery.

Green and Efficient Removal of Toxic Lead and Chromiumfrom Synthetic Leather Tannery Wastewater using Electrocoagulation

Most of leather tanneries in Pakistan dispose of tannery effluent untreated in sewage lines causing serious harmful environmental impact. Some of tanneries use conventional activated sludge process releasing large quantity of sludge and not effective for treating heavy metal in leather tanneries. The manuscript deals with implementation of electrocoagulation technology for removal of Cr and Pb from Leather tannery effluent, investigation of operating parameters current density, treatment time and pH on removal efficiency. Electrodes was made of Iron having dimension 9.5 cm x 0.6 cm x 0.4 cm and affective surface area of electrode was 76 cm&lt;sup&gt;2&lt;/sup&gt;. After conducting different experiments at various operating conditions, pH 3.5 and current density 18.8 milliamp/cm2 was found to be optimized condition for treating 1 liter of synthetic leather tannery effluent. The maximum removal efficiency of chromium and lead was obtained 87.8 % and 62.7 % respectively at pH 3.5 and current density of 18.8 milliamp/cm&lt;sup&gt;2&lt;/sup&gt;. The EDX analysis of sludge shows presence of chromium, lead and iron element in sludge and FTIR analysis shows the presence of hydroxyl functional group in sludge, it is strong evidence of iron polymer complexes formation with chromium and lead during treatment of synthetic leather tannery wastewater. Both of these analysis show strong evidence of effective electrocoagulation process. It was proved that electrocoagulation can effectively treat synthetic leather tannery effluent. The SEM analysis shows production of coagulant on surface of electrode.

Evaluation of virus removal in membrane bioreactor (MBR) and conventional activated sludge (CAS) processes based on long-term monitoring at two wastewater treatment plants

The membrane bioreactor (MBR) process always offers better wastewater treatment than conventional activated sludge (CAS) treatment. However, the difference in their efficacy of virus reduction remains unknown. To investigate this, we monitored virus concentrations before and after MBR and CAS processes over 2 years. Concentrations of norovirus genotypes I and II (NoV GI and GII), aichivirus (AiV), F-specific RNA phage genotypes I, II, and III (GI-, GII-, and GIII-FRNAPHs), and pepper mild mottle virus (PMMoV) were measured by a quantitative polymerase chain reaction (qPCR) method at two municipal wastewater treatment plants (WWTPs A and B) in Japan. Virus concentration datasets containing left-censored data were estimated by using both maximum likelihood estimation (MLE) and robust regression on order statistics (rROS) approaches. PMMoV was the most prevalent at both WWTPs, with median concentrations of 7.5 to 8.8 log10 copies/L before treatment. Log10 removal values (LRVs) of all viruses based on means and standard deviations of concentrations before and after treatment were consistently higher following MBR than following CAS. We used NoV GII as a model pathogen in a quantitative microbial risk assessment of the treated water, and we estimated the additional reductions required following MBR and CAS processes to meet the guideline of 10−6 DALYs pppy for safe wastewater reuse.

Interrelation between extracellular polymer substances (EPSs) and MPs in an MBR

Nowadays, microplastics (MPs), as ubiquitous pollutants in aquatic ecosystems, present a major emerging threat. Wastewater treatment plants (WWTPs) are considered a hotspot of MP contamination. In this context, membrane bioreactors (MBRs), which combine conventional activated sludge processes with filtration, serve as an effective technology to remove MPs from wastewater. One of the main factors that affect MBR performance is the amount and composition of extracellular polymeric substances (EPSs) in the mixed liquor (ML). In previous studies carried out at lab-scale with model MPs, it has been found that the presence of MPs in wastewater treatment processes affect the EPS characteristics. In this work, the inter-relationship between EPSs and MPs has been investigated in a MBR at an industrial scale. Samples of the ML were taken from a WWTP during a six-month period and EPSs and MPs were analysed. It was observed that the higher the concentration of MPs, the higher the amount of EPSs were secreted by microorganisms, which seems to indicate that MPs act as an environmental stressor. Additionally, ML samples were centrifuged and the retention of MPs in the centrifuged solid (CS), which mainly depends on the size and morphology of MPs, was evaluated in relation to the amount and composition of EPSs. Remarkably, the concentration of humic acids showed a linear correlation with respect to the percentage of MPs retained in the CS. According to this, a possible mechanism based on hydrophobic interactions has been proposed as being responsible for the retention of MPs in sludge flocs.

Advancements and Challenges in Membrane Bioreactor Technology for Industrial Wastewater Treatment

Due to its success in achieving the majority of wastewater treatment objectives, Membrane Bioreactor Technology (MBR) has replaced the Conventional Activated Sludge Process (CAS) as the leading method for treating wastewater. Nowadays, the treatment of industrial wastewater become one of the world’s major concerns, MBR technologies are used more frequently. This technology has a bright future in wastewater treatment (especially industrial wastewater). In general, this article is designed to give a general view of various aspects of an MBR, with the aim of addressing and overcoming any potential drawbacks or limitations. In this work, the fouling in MBR technology its variations and mechanisms, influencing factors are also discussed in detail. However, membrane fouling is thought to be the biggest challenge this technology faces. One of the main agents that causes the fouling of the membrane is Extracellular Polymeric Substances (EPS), which results in a decrease in filterability and a decline in membrane flux, which affects the membrane lifespan. Furthermore, it looks into how to minimize membrane fouling in MBR systems and offers biological tactics to lessen the likelihood of membrane fouling in MBR technology. Finally, this work quoted also how artificial technology might help to increase removal effectiveness and prevent filtering membrane obstruction.

Mesophilic, thermophilic and thermal hydrolysis process coupled anaerobic digestion of sewage sludge: Biomethane potential, pathogen removal and energy feasibility

Conventional Anaerobic digestion is one of the most preferred sludge management techniques however, it has limitations such as low hydrolysis rate, longer retention time, larger digester volume, and reduced methane generation etc., To overcome these problems, Thermal hydrolysis process (THP) has been used as an effective pretreatment method for enhancing methane generation. However, the effect of the thermal hydrolysis process in heavy metal solubilization and methane production from high SRT (solids retention time) sludge is still not clear. Anaerobic digestion of sewage sludge sourced from sequencing batch reactor (SBR) and conventional activated sludge process (CASP) systems were evaluated under mesophilic (MAD), thermophilic (TAD), and thermal hydrolysis process (THP) mediated anaerobic digestion (AD) in terms of methane generation and, VS and pathogen removal. THP resulted in almost 38% COD solubilization for SBR and CASP sludge. Anaerobic digestion of SBR sludge resulted in methane generation of 101, 166, and 390 mL/gVS under mesophilic, thermophilic, and THP pretreatment conditions, respectively. For CASP sludge, the highest methane generation was observed for THP pretreated sludge (587 mL/gVS), followed by thermophilic (298 mL/gVS) and mesophilic digestion (241 mL/gVS). The fecal coliforms in the mesophilic and thermophilic digested SBR sludge were 3000 and 620 MPN/g, respectively, while 6100 and 740 MPN/g were found in digested CASP sludge, respectively. The THP-MAD and TAD processed SBR, and CASP sludges met the Class A sludge fecal coliforms and Salmonella density criteria of <1000 MPN/g TS (dry basis) and 3 MPN/4g TS (dry basis), respectively, over MAD processed sludges. Even though THP pretreatment resulted in the release of heavy metals, the concentration of heavy metals in the THP effluent was lesser than the limits prescribed by USEPA. The energy demand of the THP unit (160 °C, 6 bar) was estimated to be 162 MJ/m3. The energy balance analysis revealed that THP pretreatment would lead to energy self-sufficiency upon integration in a wastewater treatment plant (WWTP). This study can provide an experimental basis to apply THP pretreatment to enhance hydrolysis rate in anaerobic digesters while maximizing methane production and achieving energy benefits over MAD and TAD.

Application of algae in wastewater treatment

Nowadays, water contamination has become one of the most significant environmental issues.  The creation and use of algal biotechnology with less investment, good effect and low operating cost has garnered a lot of attention. With the ongoing development of numerous new water treatment technologies, low-cost and effective ecological governance systems have been created quickly. Its purpose is to improve the sewage purification process by improving the inorganic process of organic matter, accelerating the expansion and multiplication of microorganisms, enhancing the metabolic function of microorganisms, and promoting the proliferation of microorganisms. In this article, the removal of nitrogen, phosphorus, heavy metals, antibiotics, pathogens and pesticides by algae was introduced. Additionally, typical algae systems including immobilized algae systems, algal-bacterial symbiotic systems and combination high-rate algae pond systems used in sewage treatment and the limitations and prospects of algae technology were discussed. Algal wastewater treatment is more effective in removing nitrogen and phosphorus than conventional activated sludge processes. Aquaculture wastewater, industrial drainage, municipal sewage, and other distinct forms of water treatment processes can all benefit from the simultaneous transformation and removal of nitrogen, phosphorus, sulfur, refractory organic matter, and heavy metals in sewage that is made possible by algae technology. Engineering techniques and technological advancement will be used to create high-efficiency microalgae wastewater treatment reactors, optimize conditions, increase the utilization efficiency of microalgae biological resources, and apply microalgae to wastewater treatment, which will have a significant impact on water quality and economy.

Sulfate Radical-Based Degradation of Organic Pollutants: A Review on Application of Metal-Organic Frameworks as Catalysts.

The degradation of organic pollutants present in domestic and industrial effluents is a matter of concern because of their high persistence and ecotoxicity. Recently, advanced oxidation processes (AOPs) are being emphasized for organic pollutant removal from effluents, as they have shown higher degradation efficiencies when compared to conventional activated sludge processes. Sulfate radical-based methods are some of the AOPs, mainly carried out using persulfate (PS) and peroxymonosulfate (PMS), which have gained attention due to the ease of sulfate radical generation and the effective degradation of organic molecules. PMS is gaining more popularity because of its high reactivity and ability to generate excess sulfate radicals. PMS has been the major focus; therefore, its mechanism has been explained, and limitations have been elaborated. The involvement of metal-organic frameworks for PMS/PS activation applied to organic pollutant removal and recent advances in the application of biochar and hydrogel-assisted metal-organic frameworks have been discussed.

Life cycle assessment of sequential microbial-based anaerobic-aerobic reactor technology developed onsite for treating textile effluent

Although biological treatment of textile effluent is a preferred option for industries avoiding toxic chemical sludge production and disposal, requirement of several extra pre-treatment units like neutralization, cooling systems or additives, results in higher operational cost. In the present study, a pilot scale sequential microbial-based anaerobic-aerobic reactor technology (SMAART) was developed and operated for the treatment of real textile effluent in the industrial premises in continuous mode for 180 d. The results showed an average ∼95% decolourization along with ∼92% reduction in the chemical oxygen demand establishing the resilience against fluctuations in the inlet parameters and climate conditions. Moreover, the pH of treated effluent was also reduced from alkaline range (∼11.05) to neutral range (∼7.76) along with turbidity reduction from ∼44.16 NTU to ∼0.14 NTU. A comparative life cycle assessment (LCA) of SMAART with the conventional activated sludge process (ASP) showed that ASP caused 41.5% more negative impacts on environment than SMAART. Besides, ASP had 46.15% more negative impact on human health, followed by 42.85% more negative impact on ecosystem quality as compared to SMAART. This was attributed to less electricity consumption, absence of pre-treatment units (cooling and neutralization) and less volume of sludge generation (∼50%) while using SMAART. Hence, integration of SMAART within the industrial effluent treatment plant is recommended to achieve a minimum waste discharge system in pursuit of sustainability.

Daily Monitoring at a Full-Scale Wastewater Treatment Plant Reveals Temporally Variable Micropollutant Biotransformations.

Despite decades of micropollutant (MP) monitoring at wastewater treatment plants (WWTPs), we lack a fundamental understanding of the time-varying metabolic processes driving MP biotransformations. To address this knowledge gap, we collected 24-h composite samples from the influent and effluent of the conventional activated sludge (CAS) process at a WWTP over 14 consecutive days. We used liquid chromatography and high-resolution mass spectrometry to (i) quantify 184 MPs in the influent and effluent of the CAS process; (ii) characterize temporal dynamics of MP removal and biotransformation rate constants; and (iii) discover biotransformations linked to temporally variable MP biotransformation rate constants. We measured 120 MPs in at least one sample and 66 MPs in every sample. There were 24 MPs exhibiting temporally variable removal throughout the sampling campaign. We used hierarchical clustering analysis to reveal four temporal trends in biotransformation rate constants and found MPs with specific structural features co-located in the four clusters. We screened our HRMS acquisitions for evidence of specific biotransformations linked to structural features among the 24 MPs. Our analyses reveal that alcohol oxidations, monohydroxylations at secondary or tertiary aliphatic carbons, dihydroxylations of vic-unsubstituted rings, and monohydroxylations at unsubstituted rings are biotransformations that exhibit variability on daily timescales.

Exploring key operational factors for improving hydrogen production in a pilot-scale microbial electrolysis cell treating urban wastewater

Bioelectrochemical systems (BES) are becoming popular technologies with a plethora of applications in the environmental field. However, research on the scale-up of these systems is scarce. To understand the limiting factors of hydrogen production in microbial electrolysis cell (MEC) at pilot-scale, a 135 L MEC was operated for six months under a wide range of operational conditions: applied potential [0.8–1.1 V], hydraulic residence time [1.1–3.9 d], and temperature [18–30 °C], using three types of wastewater; synthetic (900 mg CODs L−1), raw urban wastewater (200 mg CODs L−1) and urban wastewater amended with acetate (1000 mg CODs L−1). The synthetic wastewater yielded the maximum current density (1.23 A m−2) and hydrogen production (0.1 m3 m−3 d−1) ever reported in a pilot scale MEC, with a cathodic recovery of 70% and a coulombic efficiency of 27%. In contrast, the use of low COD urban wastewater limited the plant performance. Interestingly, it was possible to improve hydrogen production by reducing the hydraulic residence time, finding the optimal applied potential or increasing the temperature. Further, the pilot plant demonstrated a robust capacity to remove the organic matter present in the wastewater under different conditions, with removal efficiencies above 70%. This study shows improved results compared to similar MEC pilot plants treating domestic wastewater in terms of hydrogen production and treatment efficiency and also compares its performance against conventional activated sludge processes.

In-situ sludge degradation and kinetics of a full scale modified activated sludge system achieving near zero sludge production

This work reports on the performance of a full scale modified AS system that consists of anaerobic/anoxic/oxic and a settler with internal waste activated sludge (WAS) recycle that achieves sludge reduction through in situ cell lysis. This modification is termed as sludge process reduction activated sludge (SPRAS) process. The SPRAS plant achieved significant sludge reduction with sludge yield of 0.0823 kg TSS/kg COD which is much lower than the sludge yield of a conventional activated sludge process of 0.3–1.2 kg TSS/kg COD. The TSS concentration in the SPRAS tank was nearly constant at 4500 mg/L showing that there was no sludge build up, a sludge volume index of 80–120 mg/L implied adequate sludge settling ability in the settling chamber which facilitated sludge separation for subsequent degradation through anaerobic digestion. In addition, the process achieved ammonia and COD reductions above 85 %. Comparative FTIR analysis of the sludge in the anaerobic and oxic chambers indicated degradation of the proteinaceous biomass cell wall in the anaerobic chamber leading to release of carbohydrates that could easily be degraded in the oxic chamber. The maximum sludge yield and sludge decay coefficient were calculated as 0.103 kg TSS/kg COD and 0.0015 thus the technology is suitable for handling municipal wastewater at minimal sludge handling cost.

Multi-parameter control-based operation strategy for mainstream deammonification in an integrated anaerobic biofilm reactor-step feed MBR

The mainstream deammonification of municipal wastewater has been recognized as one of the greatest challenges in wastewater engineering. The conventional activated sludge process has disadvantages of high energy input and sludge production. To tackle this situation, an innovative A-B process, where an anaerobic biofilm reactor (AnBR) functioned as the A stage for energy recovery, and a step-feed membrane bioreactor (MBR) functioned as the B stage for mainstream deammonification, was constructed for carbon-neutral wastewater treatment. For addressing the challenge associated with selective retention of ammonia-oxidizing bacteria (AOB) over nitrite oxidizing bacteria (NOB), a multi-parameter control-based operation strategy was developed with synergistic control of influent COD redistribution, dissolved oxygen (DO) concentration and sludge retention time (SRT) in the innovative AnBR – step-feed MBR system. Results showed that more than 85% of wastewater COD could be removed with the direct production of methane gas in the AnBR. A relatively stable partial nitritation, which is a prerequisite of anammox, was achieved with the successful suppression of NOB, leading to 98% of ammonium-N and 73% of total nitrogen removed. Anammox bacteria could well survive and enrich in the integrated system, and the contribution of anammox to the total nitrogen removal was more than 70% at optimal conditions. Reactions network involved in the nitrogen transformation in the integrated system was further constructed through the mass balance and microbial community structure analyses. Consequently, this study demonstrated a practically feasible process configuration with high operation and control flexibility towards stable mainstream deammonification of municipal wastewater.