Effects of sodium hypochlorite concentration on the methanogenic activity in an anaerobic fluidized membrane bioreactor

Impact of carbon-based conductive materials on performance and microbial community composition during anaerobic digestion of butanol-octanol wastewater

Butanol-octanol wastewater (BOW) from coal syngas conversion with hazardous and high salinity could hinder anaerobic digestion (AD). The carbon-based conductive materials (CCM) appear viable for enhancing the AD capability of BOW. Nevertheless, the potential mechanisms of different CCM types on AD of BOW remain unclear. The three different morphologies of CCM, powdered activated carbon (PAC), granular activated carbon (GAC), and carbon fiber cloth (CFC), were employed to improve methane conversion rate in AD of actual BOW. Results indicated that, compared to other carbon materials, more aromatic functional groups on the surface of GAC promoted electron transfer and notably increased degradation of 3-heptanone in BOW and methanogenic. Microbial community structure analysis showed Geobacter on GAC increased to 30.99 %, while Syntrophomonas and Methanosaeta in the sludge increased by 5.05 % and 7.7 %, respectively. The methane conversion rate of BOW was increased by promoting direct interspecies electron transfer (DIET) through GAC.

Evaluating performance of nano-Fe3O4 modified granular activated carbon assisted wastewater treatment in anaerobic fluidized membrane bioreactor

Magnetic granular activated carbon (MGAC), a nano-Fe₃O₄ modified granular activated carbon, was used as the carrier in an anaerobic fluidized-bed membrane bioreactor (AFMBR) to promote domestic wastewater treatment efficiency and alleviate membrane biofouling. Chemical oxygen demand (COD) removal reached 89 ± 2.6% with the effluent concentration of 20 ± 3.9 mg/L in the MGAC-AFMBR, while it was 28 ± 5.2 mg/L in AFMBR at hydraulic retention time (HRT) of 4 h. Total nitrogen (TN) removal was also enhanced by 4.0% with MGAC. An increased proportion of Chloroflexi and Bacteroidetes in the sludge may be responsible for improved treatment performance. MGAC reduced the protein and polysaccharide content in extracellular polymeric substances (EPS) by 9.8% and 8.1%, respectively. Besides, Bacteroidetes and Proteobacteria abundance decreased by 4.0% and 16.6% in the membrane cake layer with MGAC addition. Therefore, the high-quality effluent and low membrane biofouling of AFMBR was sustained by MGAC.

A new hybrid ensemble approach for the prediction of effluent total nitrogen from a full-scale wastewater treatment plant using a combined trickling filter-activated sludge system

In this study, different K-nearest neighbors (KNN), support vector regression (SVR), decision tree (DT), and random forest (RF) algorithms integrated with the Bayesian optimization algorithm (BOP) have been applied as novel hybrid modeling/optimization tools to predict the total nitrogen in treated wastewater of Southern Tehran Wastewater Treatment Plant (STWWTP). In order to enhance the outcomes of hybrid models, the chosen sub-models (the best and least correlated hybrid models) were used to generate voting average and stacked regression ensemble models. Throughout the preprocessing step, two alternative scenarios were used to handle missing values from the samples, including elimination versus estimation via linear interpolation. The results of this research demonstrated that ensemble models were better than individual hybrid models, although not all ensemble models were superior to single models. The results also revealed that the stacking regression ensemble model using KNN-BOP and SVR-BOP as sub-models was the most superior model among the developed models, with the coefficient of determination (R²) = 0.640, root mean squared error (RMSE) = 2.378, and mean absolute error (MAE) = 1.838 on the test data. The best hybrid ensemble model that can accurately predict the concentration of total nitrogen (TN) in the effluent can give people a heads-up about water pollution caused by eutrophication before it gets bad.

Technological advancements in valorisation of industrial effluents employing hydrothermal liquefaction of biomass: Strategic innovations, barriers and perspectives

Hydrothermal liquefaction (HTL) is identified as a promising thermochemical technique to recover biofuels and bioenergy from waste biomass containing low energy and high moisture content. The wastewater generated during the HTL process (HTWW) are rich in nutrients and organics. The release of the nutrients and organics enriched HTWW would not only contaminate the water bodies but also lead to the loss of valued bioenergy sources, especially in the present time of the energy crisis. Thus, biotechnological as well as physicochemical treatment of HTWW for simultaneous extraction of valuable resources along with reduction in polluting substances has gained significant attention in recent times. Therefore, the treatment of wastewater generated during the HTL of biomass for reduced environmental emission and possible bioenergy recovery is highlighted in this paper. Various technologies for treatment and valorisation of HTWW are reviewed, including anaerobic digestion, microbial fuel cells (MFC), microbial electrolysis cell (MEC), and supercritical water gasification (SCWG). This review paper illustrates that the characteristics of biomass play a pivotal role in the selection process of appropriate technology for the treatment of HTWW. Several HTWW treatment technologies are weighed in terms of their benefits and drawbacks and are thoroughly examined. The integration of these technologies is also discussed. Overall, this study suggests that integrating different methods, techno-economic analysis, and nutrient recovery approaches would be advantageous to researchers in finding way for maximising HTWW valorisation along with reduced environmental pollution.

Sodium hypochlorite induced inhibition in anaerobic digestion and possible approach to maintain methane fermentation performance

Since sodium hypochlorite (NaClO), a commonly used chemical to deal with membrane fouling, is toxic to microorganisms, it is a major concern in the membrane cleaning process. In this study, the concentration-dependent effects of NaClO (0-9 g/L) on the biodegradation performance and microbial activity were investigated via batch experiments. The methane production (obtained approximately 140 mL) and microbial community revealed by principal coordinates analysis were almost unaffected when the NaClO concentration ranged between 0 and 3 g/L. A follow-up batch experiment was conducted and revealed that the microbial products could help protect or recover the activity of anaerobic microorganisms at a high NaClO concentration of 10 g/L. Additionally, correlation analysis was used to investigate the associations between the 15 major bacterial genera. Moreover, the microbial analysis results indicated that the top 10 operational taxonomic units most affected by NaClO were primarily coryneform and filamentous bacteria.

A critical review on biogas production from edible and non-edible oil cakes

The circular economy is at the core of sustainable development. The generation of biogas from the massive quantity of agricultural waste biomass is one of the critical drivers of the circular economy. Biogas has enormous renewable energy potential and has multitudes of applications in today's energy-intensive society. Oil cakes, a known Agri-waste, are the by-product of oil processing, and are rich in nutrients. The edible oil cakes mostly have been used as a cattle feed; however, non-edible oil cakes do not find many applications. Their production is continuously escalating as non-edible oils are increasingly used in biodiesel production. Recently, there is a lot of emphasis on biogas production from these oil cakes. This paper reviews in detail biogas production from both edible and non-edible oil cakes. Chemical composition and various other applications of the cakes are also reviewed in brief. The survey illustrates that multiple parameters such as inoculum sources, co-digestion and reactor design affect the biogas production. All those factors, along with biogas upgrading and the economy of the process, are reviewed. Finally, future research opportunities are suggested to improve the viability of the biogas production from oil cakes.

Nutrient removal from domestic wastewater: A comprehensive review on conventional and advanced technologies

Nitrogen and phosphorous are indispensable for growth and vitality of living beings, hence termed as nutrients. However, discharge of nutrient rich waste streams to aquatic ecosystems results in eutrophication. Therefore, nutrient removal from wastewater is crucial to meet the strict nutrient discharge standards. Similarly, nutrient recovery from waste streams is vital for the realization of a circular economy by avoiding the depletion of finite resources. This manuscript presents analysis of existing information on different conventional as well as advanced treatment technologies that are commonly practiced for the removal of nutrient from domestic wastewater. First, the information pertaining to the biological nutrient removal technologies are discussed. Second, onsite passive nutrient removal technologies are reviewed comprehensively. Third, advanced nutrient removal technologies are summarized briefly. The mechanisms, advantages, and disadvantages of these technologies along with their efficiencies and limitations are discussed. An integrated approach for simultaneous nutrient removal and recovery is recommended. The fifth section of the review highlights bottlenecks and potential solutions for successful implementation of the nutrient removal technologies. It is anticipated that the review will offer an instructive overview of the progress in nutrient removal and recovery technologies and will illustrate necessity of further investigations for development of efficient nutrient removal and recovery processes.

Up-concentration processes of organics for municipal wastewater treatment: New trends in separation

Carbon neutrality is a pressing goal for the whole society. Over 20% of municipality electrical energy on public utilities was consumed by the operation of wastewater treatment plants (WWTPs). Up-concentration of organic matters and maximum energy recovery is essential for a more sophisticated municipal wastewater management. Chemical coagulation and biological adsorption have been used to achieve efficient carbon capture, while separation is an overlooked step. It may lead to poor effluent quality, as well as consume most of the time and volume. The introduction of new driving forces, such as pressure and magnetism, significantly improved the retention rate and speed, respectively. In this paper, recent works were comprehensively reviewed and a horizontal comparison was conducted from aspects of separation speed, retention rate, concentrate characteristics and economic costs. This review also discussed the selection of technologies under different conditions. Finally, the practical application, fouling mitigation with considering the value of the concentrate, identification of unique concentrate characteristics, and the establishment of an evaluation system was suggested as core issues for future researches. This review will promote the development of an energy-efficient wastewater treatment system with up-concentration processes.

Combined Effect of Activated Carbon Particles and Non-Adsorptive Spherical Beads as Fluidized Media on Fouling, Organic Removal and Microbial Communities in Anaerobic Membrane Bioreactor

The combined effect of acrylonitrile butadiene styrene (ABS) spherical beads and granular activated carbon (GAC) particles as fluidized media on the performance of anaerobic fluidized bed membrane bioreactor (AFMBR) was investigated. GAC particles and ABS beads were fluidized together in a single AFMBR to investigate membrane fouling and organic removal efficiency as well as energy consumption. The density difference between these two similarly sized media caused the stratified bed layer where ABS beads are fluidized above the GAC along the membrane. Membrane relaxation was effective to reduce the fouling and trans-membrane pressure (TMP) below 0.25 bar could be achieved at 6 h of hydraulic retention time (HRT). More than 90% of soluble chemical oxygen demand (SCOD) was removed after 80 d operation. Biogas consisting of 65% of methane was produced by AFMBR, suggesting that combined use of GAC and ABS beads did not have any adverse effect on methane production during the operational period. Scanning Electron Microscope (SEM) examinations showed the adherence of microbes to both media. However, 16S rRNA results revealed that fewer microbes attached to ABS beads than GAC. There were also compositional differences between the ABS and GAC microbial communities. The abundance of the syntrophs and exoelectrogens population on ABS beads was relatively low compared to that of GAC. Our result implied that syntrophic synergy and possible occurrence of direct interspecies electron transfer (DIET) might be facilitated in AFMBR by GAC, while traditional methanogenic pathways were dominant in ABS beads. The electrical energy required was 0.02 kWh/m3, and it was only about 13% of that produced by AFMBR.

Treatment technologies for emerging contaminants in wastewater treatment plants: A review

The "emerging contaminants" (ECs) are predominantly unregulated anthropogenic chemicals that occur in air, soil, water, food, and human/animal tissues in trace concentrations. The ECs are persistent in the environment, capable of perturbing the physiology of target receptors and, therefore, are regarded as contaminants of emerging environmental concerns in recent years. The prominent classes of ECs include pharmaceuticals and personal care products (PCPs), surfactants, plasticizers, pesticides, fire retardants, and nanomaterials. Some of the ECs with harmful effects on endocrine systems have been recognized as endocrine disrupting chemicals (EDCs). Since the 1990s intensive research has been done covering environmental occurrence, fate, ecological effects, and treatment technologies of ECs. However, a comprehensive summary of the EC removal techniques, particularly in wastewater treatment plants (WWTPs) are limited. Though the WWTPs are inefficient when it comes to ECs removal, they act as primary barriers against the spread of ECs. Therefore, this paper reviews the treatment technologies currently engaged for ECs removal in WWTPs for further possible upgrades of the existing designs. Results of this review indicate that the fate and distribution of ECs can be approximately estimated based on physicochemical properties like octanol-water partitioning coefficient (e.g., log K_OW > 4, maximum sorption potential) and solid-water distribution coefficient [e.g., K_d < 300-500 L/kg MLSS (mixed liquor suspended solids), insignificant sorption into sludge]. Biodegradation potential of ECs can be predicted from biodegradation constant values (e.g., K_bio < 0.01 = low biodegradation and >10 = high biodegradation). In WWTPs, the EC removal efficiency varies in the range of 20-50%, 30-70%, and >90% during the primary, secondary, and tertiary treatment steps, respectively. Tertiary treatment technologies are considered as the most suitable alternatives for ECs treatment, but complete ECs removal is yet to be achieved. Further advancements in the treatment technologies will unquestionably be necessary in the future.

A brief review of anaerobic membrane bioreactors emphasizing recent advancements, fouling issues and future perspectives

This review summarizes the recent development and studies of anaerobic membrane bioreactor (AnMBR) to control fouling issues. AnMBR is an emerging waste water treatment technology mainly because of its low sludge residual, high volumetric organic removal rate, complete liquid-solid separation, better effluent quality, efficient resource recovery and the small footprint. This paper surveys the fundamental aspects of AnMBRs, including its applications, membrane configurations, and recent progress for enhanced reactor performance. Furthermore, the membrane fouling, a major restriction in the practical application of AnMBR, its mechanism and antifouling strategies like membrane cleaning, quorum quenching, ultrasonic treatment, membrane modifications, and antifouling agents are briefly discussed. Based on the review, the key issues that require urgent attention to facilitate large scale and integrated application of AnMBR technology are identified and future research perspectives relating to the prevalent issues are proposed.

Process optimization and energy analysis of vacuum degasifier systems for the simultaneous removal of dissolved methane and hydrogen sulfide from anaerobically treated wastewater

The control of dissolved methane (CH₄) and hydrogen sulfide (H₂S) emissions in anaerobic effluents is essential for minimizing the environmental implications of greenhouse gases, odor, and carbon footprint, as well as for preventing energy loss in the form of unrecovered dissolved methane. This study assessed the feasibility of a vacuum degasifier for the removal of CH₄ and H₂S from staged anaerobic fluidized membrane bioreactor (SAF-MBR) effluent. The optimization results showed that the efficiency of the nozzle fitted degasifiers were superior to the media packed ones. In three-stage vacuum degasifiers at a -0.8 bar vacuum pressure, H₂S removal was mostly pH dependent and 88% removal efficiency was achieved with an initial concentration of 13.6 mg/L. Methane removal was dependent primarily on the number of degasifier units, and approximately 94% efficiency was achieved in a three-stage degasifier. Energy balance analysis showed that energy production exceeded the system energy requirements with 0.05-0.07 kWh/m³ of surplus energy. These results provide deep insights into this new technology for simultaneous removal of dissolved CH₄ and H₂S, which can be referred for potential future applications.

Optimization of In Situ Backwashing Frequency for Stable Operation of Anaerobic Ceramic Membrane Bioreactor

The cost-effective and stable operation of an anaerobic ceramic membrane bioreactor (AnCMBR) depends on operational strategies to minimize membrane fouling. A novel strategy for backwashing, filtration and relaxation was optimized for stable operation of a side stream tubular AnCMBR treating domestic wastewater at the ambient temperature. Two in situ backwashing schemes (once a day at 60 s/day, and twice a day at 60 s × 2/day) maintaining 55 min filtration and 5 min relaxation as a constant were compared. A flux level over 70% of the initial membrane flux was stabilized by in situ permeate backwashing irrespective of its frequency. The in situ backwashing by permeate once a day was better for energy saving, stable membrane filtration and less permeate consumption. Ex situ chemical cleaning after 60 days’ operation was carried out using pure water, sodium hypochlorite (NaOCl), and citric acid as the order. The dominant cake layer was effectively reduced by in situ backwashing, and the major organic foulants were fulvic acid-like substances and humic acid-like substances. Proteobacteria, Firmucutes, Epsilonbacteria and Bacteroides were the major microbes attached to the ceramic membrane fouling layer which were effectively removed by NaOCl.

Evaluation of the cytotoxic potential of sodium hypochlorite using meristematic root cells of Lens culinaris Med

The present investigation was designed to monitor the cytotoxic potential of Sodium Hypochlorite using lentil (Lens culinaris) as a bioindicator of toxicity. Sodium hypochlorite (NaClO), is a chemical compound that is used mainly for its disinfectant properties, its effect is widely toxic, which is why it is marketed in low concentrations and it is also a component in various products such as agrochemicals. In the present study the L. culinaris seeds were exposed to different NaClO dose 0, 0.2, 1, 3, 5 and 7 mg L^-1 during 24, 48 and 72 h; timeslots in which the root growth was also studied. The cytotoxic potential of NaClO was determined by calculating the mitotic index (MI), calculating cellular anomalies (CA) and observing the longitudinal growth of the roots during the various time periods. The radicular growth was prolonged and it was observed that there was a greater growth at the dose of 1 and 7 mg L^-1 in the time of 72 h. The cytotoxic effects could be analyzed in the mitotic index, since the higher the concentration, the lower the mitotic index, as observed in the dose of 7 mg L^-1 where a reduction of the mitotic index of the meristematic cells is observed. The results indicate that NaClO has a cytotoxic effect that induces various types of chromosomal abnormalities. This indicates that Sodium Hypochlorite has a cytotoxic effect according to the increase in its dose. Therefore, Lens culinaris turned out to be a kind of appropriate bioindicator to study the cytotoxic effects of various potentially toxic substances.