H Hydraulic Retention Time Research Articles

Valorization of paper-mill sludge laden with 2-chlorotoluene using hydroxyapatite@biochar nanocomposite to enrich methanogenic community: A techno-economic approach

While several studies have investigated the anaerobic digestion of paper-mill sludge (PMS), this technology suffers from nutrient insufficiency, inhibition by aromatic compounds, and low bio-CH4 yield. Hence, PMS was anaerobically co-digested with chicken manure (CM) and supplemented by hydroxyapatite@biochar (HAP@BC) nanocomposite for enhancing 2-chlorotoluene degradation and enriching the methanogenic archaea. Multiple continuous stirred tank reactors (CSTRs) were operated at 12.6 h hydraulic retention time (HRT), using PMS (R1), CM (R2), PMS + CM (R3), PMS + CM+100 mg HAP/L (R4), and PMS + CM+100 mg HAP@BC/L (R5). The maximum bio-CH4 yield of 147.5 ± 9.1 mL/g COD and 2-chlorotoluene removal of 91.2 ± 6.8 % were obtained from R5, experiencing a sufficient C/N ratio of 14.7 and the highest activities of acidogenesis (42.0 %), acetogenesis (37.9 %), and methanogenesis (42.1 %). The abundances of Euryarchaeota, Bacteroidota, and Chloroflexi at the phylum level, and Pseudomonas, and Bacillus at the genus level could highly contribute to the dechlorination mechanism and acetate transformation into CH4. This biomass-to-bioenergy project (10 m3/d capacity) could benefit from pollution reduction, biogas recovery, and carbon credit, giving 5.6 yr payback-period, 3503 USD net present value, and 12.1 % internal rate of return. Because R5 exhibited an efficient techno-economic anaerobic biodegradation performance, future studies are required to optimize its HRT condition and HAP@BC dosage.

Anaerobic treatment of low-strength municipal wastewater with electroactive magnetite-embedded granules under mainstream conditions

This study examined the potential for the anaerobic treatment of low-strength wastewater (250 mg chemical oxygen demand/L) using expanded granular sludge bed (EGSB) with conductive magnetite-embedded granules (MEGs) under mainstream conditions (25°C). The inclusion of magnetite, with high specific gravity and conductivity, enhanced the settleability, structural stability, and electron transfer capability of MEGs compared to granules without it. Within the hydraulic retention time (HRT) range of 4–12 h, the MEG-EGSB reactors maintained superior treatment performance, along with comparable or higher methane production, compared to the control EGSB reactors lacking MEGs. This performance enhancement was more pronounced under conditions of higher hydraulic and organic loading. The MEG-EGSB reactors achieved approximately 90% organic removal efficiency at 8–12-h HRTs, a range comparable to that of the aerobic activated sludge process, with minimal loss of magnetite. The results from RNA-based microbial community analysis, alone with the consistently higher methane content in the biogas from MEG-EGSB reactors, supported the potential development of electric syntrophy between exoelectrogenic bacteria and electrotrophic methanogens in electroactive MEGs. This capability of MEGs to promote electro-syntrophic methanogenesis could potentially enhance methanogenic degradation of organic matter. The overall findings suggest that the MEG-EGSB process is a promising candidate for anaerobic municipal wastewater treatment.

Valorization of organic carbon in primary sludge via semi-continuous dark fermentation: First step to establish a wastewater biorefinery

In this study, lab-scale, bench-scale, and pilot-scale experiments were carried out to optimize short-chain fatty acids production from primary sludge. Batch tests showed the requirement of short retention times and semi-continuous operation mode showed a plateau of maximum daily productivity at 36-hours hydraulic retention time with minimal methanation. Optimization from pH 5 to pH 10 at 36 h-hydraulic retention time under long-term semi-continuous operating mode revealed that production of short-chain fatty acids was pH dependent and highest yields could be achieved at pH 7 by establishing optimum redox conditions for fermentation. Pilot-scale experiments at 32 °C showed that daily productivity (3.1 g∙Lreactor-1∙dHRT-1) and yields (150 mg∙gVS-1; OLR = 21 gVS∙Lreactor-1∙dHRT-1; pH 7) of short-chain fatty acids could be significantly improved, specifically for acetic and propionic acids. From these results, a robust dark fermentation step for recovery of valuable products from the solids treatment step in a biorefinery can be achieved.

Anode biomass rather than soluble organic matter is fuel for electricity production in microbial fuel cell at longer hydraulic retention time

This study presents a novel method for independently calculating organic matter (OM) removal and electricity generation in a microbial fuel cell (MFC) treating sewage. This methodology used OM concentration as the exclusive variable for input, facilitating the prediction of electricity generation with variable Coulombic efficiency. The employed MFC, of tubular design, incorporates an air core surrounded by a carbon-based cathode, an anion exchange membrane, nonwoven graphite fabric, and encircled by twelve carbon brush anodes. This setup successfully reduced chemical oxygen demand (COD) from 180 to 50 mg L−1 and biological oxygen demand (BOD) from 84 to 15 mg L−1 within a 35 h hydraulic retention time (HRT). The resulting effluent BOD satisfies Japanese wastewater treatment standards. In the early HRT phase, the MFC exhibited rapid OM reduction, followed by a stabilization of OM concentration. Despite varying HRTs and the sustained OM levels at prolonged HRTs, the MFC consistently generated 0.29 ± 0.14 A m−2. This apparent contradiction prompted the consideration of additional OM sources from the anode biomass (Cb). Calculating electricity production based on OM concentration rather than OM degradation was achieved by assessing anode resistance (RAn) across different levels of OM supplementation, employing the Butler–Volmer equation. This approach, incorporating considerations for Cb and RAn, accurately reproduced MFC performance. It was observed that OM supplementation from Cb constituted 50% at 11 h HRT and escalated to 90% at 27 h HRT. Further analysis, including 16S rRNA gene-based microbial community profiling, indicated that higher cathode resistance (RCat) at 1.0 Ω m2, compared to a minimum RAn of 0.10 Ω m2, favored methanogenesis over electrogenesis on the carbon brushes. This finding underscores the importance of reducing RCat and minimizing electrode distance, coupled with enhancing the specific surface area of both electrodes, as crucial factors for the advancement of MFC technology.

Co-digestion of solid-liquid waste from citrus agroindustrial: Effect of hydraulic retention time and organic loading rate on H2 production in a long-term continuous operation leach bed reactor

The Leach Bed Reactor (LBR) application is a promising alternative for the anaerobic digestion of solid waste and wastewater. In this study, the LBR was continuously operated for 160 days in four different phases, for co-fermentation of solid and liquid waste from the citrus agroindustry, at 37 °C, evaluating the effect of hydraulic retention time (HRT) and organic loading rate (OLR). The maximum volumetric hydrogen production (VHPR) was observed at an HRT of 12h (958.3 mLH2.L-1.d-1); however, the highest hydrogen yield (HY) was identified at an HRT of 24h (104.9 mLH2.g-1CHO). Based on the metabolic characteristics of microorganisms identified in higher relative abundance, by 16S rRNA sequencing, such as Lactobacillus, Caproicoproducens, Bifidobacterium, Olsenella, and Solobacterium, an occurrence of chain elongation pathways in the production of butyric and caproic acids was inferred, with hydrogen production resulting from the lactic acid oxidation. The maximum electricity production potential of 16.3 kWh.m-3 liquor was estimated.

Microbiological characterization of biofilm from different immobilization structures used in submersed aerobic biofilters in domestic effluent treatment at the city of Joinville, Brazil.

The objective of this work was to develop a polymeric structure for a biofiltration unit of domestic effluents through microbiological immobilization, capable of promoting the efficient removal of pollutants, meeting local/national Brazilian standards and/or legislation while providing low environmental impact on their production. Four different structures were tested, namely, polypropylene casings without filling material (TF1); polypropylene casings filled with expanded polystyrene grains (TF2); polypropylene casings, filled with polyurethane foam (TF3); and polypropylene casings, filled with polyvinyl chloride pellets (TF4). A flow of 0.216 m3 d-1 was applied to the system, and the biofilters operated in sequential batches with a hydraulic retention time of 6h. The efficiency potential of the four immobilization structures was verified regarding biochemical and chemical oxygen demand, total ammoniacal nitrogen and total phosphorus. Microbiological analysis of the formed biofilm, performed with the 16S library sequencing method, with amplification of the 16S rRNA V3 and V3-V4 genomic regions, showed a high diversity of microbiological colonization in the four immobilization structures, with better results and consequently greater community stability in TF2. It is recommended using the filter bed made up of unfilled casings, followed by the one filled with expanded polystyrene grains.

Pyrite-based denitrification combined with electrochemical disinfection to remove nitrate and microbial contamination from groundwater

Nitrate and microbial contamination of groundwater can occur in countries that face intense urbanization and inadequate sanitation. When groundwater is the main drinking water source, as is often the case in such countries, the need to remove these contaminants becomes acute. The combination of two technologies is proposed here, a biological step to denitrify and an electrochemical step to disinfect the groundwater, thereby aiming to reduce the chemical input and the footprint of groundwater treatment. As such, a pyrite-based fluidized bed reactor (P-FBR) was constructed to autotrophically denitrify polluted groundwater. The P-FBR effluent was disinfected in an electrochemical cell with electrogenerated Cl2. Nitrate was removed with 79% efficiency from an initial 178 mg NO3− L−1 at an average denitrification rate of 171 mg NO3− L−1 d−1, with 18 h hydraulic retention time (HRT). The electrochemical unit achieved a 3.8-log reduction in total coliforms with a 41.7 A h m−3 charge density.

Anaerobic degradation of hexachlorocyclohexane: Factors influencing the reactor start-up

This study examined the anaerobic degradation of technical-hexachlorocyclohexane (t-HCH)-a persistent organic pollutant (POP), using a batch reactor and the influence of pH, active biomass as volatile suspended solids (VSS), total suspended solids, total organic carbon, chloride release, and elemental composition on an Upflow Anaerobic Sludge Blanket (UASB) reactor start-up. Chloride release, a direct indicator of HCH degradation, was measured to confirm the process. During the initial sludge acclimatization, only 49.23 % degradation efficiency was seen after 45 days with an initial concentration of 1.0 g l−1. However, when electron donors and co-substrates were added to the sludge, the degradation time was shortened to 15 days with an increase in efficiency up to 60.17 %. When this adapted sludge was taken in a UASB reactor start up at 100 mg l−1 HCH, this degradation effectiveness was significantly improved when organic loading rate (OLR) was decreased to 50 mg l−1 d−1 assuming 48 h hydraulic retention time (HRT) in a UASB reactor start up at 100 mg l−1 HCH. During the original UASB reactor start-up, 92.37 %, 90.64 %, 85.72 %, and 83.26 % degradation of the alpha, gamma, beta, and delta isomers, with evidence of pentachlorocyclohexene as a transitory intermediate was observed. The major determining variables for reactor start-up were found to be neutral pH, mesophilic temperature, addition of co-substrate (glucose), VSS, HRT, and OLR. The study's innovation is that it examines the efficacy of the degradation process during sludge acclimatization and gives useful details about the variables to consider when starting up a UASB reactor. This research gives a biodegradation trend, which may be required before venturing for anaerobic degradation of recalcitrant substances like t-HCH.

Effects of Temperature and Water Types on the Decay of Coronavirus: A Review

The analysis of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) gene copy numbers in wastewater samples can provide quantitative information on Coronavirus Disease-19 (COVID-19) cases within a sewer catchment. However, many wastewater-based epidemiology (WBE) studies have neglected virus decay during the wastewater transportation process in sewers while back-calculating COVID-19 prevalence. Among various sewer condition parameters, wastewater temperature and dilution by fresh/saltwater infiltration may result in a significant change to the virus decay, in terms of both infectivity and Ribonucleic Acid (RNA). This paper reviewed the literature to identify and discuss the effects of temperature and water types (i.e., wastewater, freshwater, and seawater) on coronavirus decay based on the decay rate constants that were collected from published papers. To evaluate the importance of virus decay, a sensitivity analysis was then conducted with decay rates of SARS-CoV-2 RNA based on a WBE back-calculation equation. Finally, the decay rates of coronavirus in wastewater were also compared with those of other viruses to further understand the difference among virus species. The decay of SARS-CoV-2 RNA was found to be less impacted by temperature variation than viable coronaviruses. Nevertheless, WBE back-calculation was still sensitive to the RNA decay rates increased by warm wastewater (i.e., over 26 °C), which could lead to a two-times higher relative variance in estimated COVID-19 prevalence, considering the wastewater temperature variation between 4 and 37 °C in a sewer catchment with a 12-h hydraulic retention time. Comparatively, the sensitivity of the WBE estimation to the enveloped SARS-CoV-2 was greater than nonenveloped enteric viruses, which were less easily degradable in wastewater. In addition, wastewater dilution by stormwater inflow and accompanied cold weather might alleviate the decay of coronavirus infectivity, thus increasing the potential risk of COVID-19 transmission through wastewater. Overall, this paper aims to better understand the impact of in-sewer processes on coronavirus decay and its potential implications for WBE. The outcome could quantitatively inform WBE and improve awareness of the increased risk of COVID-19 infection via wastewater during heavy rainfall events. Given the identified scarcity of data available for coronavirus decay in salt water or with chemical additions, future research on the fate of SARS-CoV-2 subjected to chemical dosing for sewer or wastewater treatment plant operations is recommended.

Stigmasterol Removal by an Aerobic Treatment System.

Stigmasterol is a phytosterol contained in kraft mill effluent that is able to increase over 100% after aerobic biological treatment. This compound can act as an endocrine disrupter as its structure is similar to that of cholesterol. Furthermore, stigmasterol contained in kraft mill effluent shows high toxicity (25-fold more than β-sitosterol) to aquatic organisms such as Daphnia magna. However, the operation of the aerobic treatment and biomass adaptation could be affecting their removal. The performances of activated sludge (AS), aerated lagoon (AL), and moving bed biofilm reactors (MBBR) are compared to remove the stigmasterol contained in kraft mill effluent. The AL operates at a hydraulic retention time of 6h and removes up to 90% of phytosterols. So, a 96% of stigmasterol is removed by AL when the sterol retention load is 0.6mg/L · d. However, stigmasterol concentrations increase from 29% to 37% at a low stigmasterol load rate (0.2mg/L · d). On the other hand, the stigmasterol is removed between 65% and 87% by an AS under a hydraulic retention time of 3h. Moreover, a 100% of stigmasterol can be removed by the MBBR when the hydraulic retention time is 2days.

Pilot-scale treatment of municipal garbage mechanical dewatering wastewater by an integrated system involving partial nitrification and denitrification

The municipal solid waste (MSW) with high water content can be pre-treated by the mechanical dewatering technology to significantly decrease the leachate generation in sequential landfill treatment or to improve the efficiency for solid waste incineration, which has attracted great concerns recently. However, the generated mechanical dewatering wastewater (MDW) containing high organics and nitrogenous content has been one of the big challenges for the sustainable treatment of MSW. In this study, a pilot-scale integrated system composed of physiochemical pretreatment, anaerobic sequencing batch reactor (ASBR), partial nitrification SBR (PN-SBR), denitrification SBR (DN-SBR), and UV/O3 advanced oxidation process, with a capacity of 1.0 m3/d to treat MDW containing over 34000 mg-chemical oxygen demand (COD)/L organics pollutant and 850 mg/L NH4+-N, was successfully developed. By explorations on the start-up of this integrated system and the process conditions optimization, after a long-term system operation, the findings demonstrated that this integrated system could reach the removal efficiency in the COD, NH4+-N and total nitrogen (TN) in the MDW of 99.7%, 98.2% and 96.9%, respectively. Partial nitrification and denitrification were successfully obtained for the TN removal with the nitrite accumulation rate of over 80%. The treatment condition parameters were optimized to be 800 mg/L polyaluminum chloride (PAC) and 2 mg/L polyacrylamide (PAM) under a pH of 9 for pretreatment, 36 h hydraulic retention time (HRT) for ASBR, 24 h for PN-SBR, and 2 h for UV/O3 unit. The organic sources in the MDW were also found to be feasible for the DN-SBR. Consequently, the resulting final effluent was stably in compliance with the discharge standard with high stability and reliability.

Treatment of High Nutrient-Loaded Wastewater in a Constructed Floating Wetland with Different Configurations: Role of Lantana Biochar Addition

Constructed wetlands (CW) with carbon stock in substrate matrix show high efficiency in wastewater nutrient removals. In this study, five batch-scale CW setups with varying Lantana weed biochar (BC) doses (5, 10, and 15%) in substrate matrix were established and changes in high nutrient-loaded wastewater parameters, ammonium N (NH4+-N), chemical oxygen demand (COD), nitrate (NO3-N), sulfate (SO4−2), and phosphate (PO4−3), were monitored for 240 h hydraulic retention time (HRT). BC amount directly affected the removal mechanism of CWs and a significant reduction in COD (>92.71%) was recorded. CW setup with a 15% BC dose showed the maximum removal of PO4−3 (79.06%), NH4+-N (78.79%), SO4−2 (67.93%), and NO3-N (77.42%) from wastewater. The theory of BC facilitated physical removal, microbial facilitation, and chemical kinetics improvements are proposed for better removal of wastewater nutrients in studied CWs. Research results could be utilized to design a low-cost domestic wastewater treatment facility using BC for rural areas under a decentralized water treatment program.

Phytoremediation potential of Schumannianthus dichotomus in vertical subsurface flow constructed wetland

Schumannianthus dichotomus (Murta) is a naturally abundant wetland plant species in Bangladesh that has significant economic and aesthetic values. This species is perennial, and fast-growing in the nutrient-abundant swamp and marshes, moreover, it can thrive in a shaded and semi-shaded environment. Although it has all the potential to be a prominent Constructed Wetlands (CW) plant, no considerable study has yet been reported on the phytoremediation potential of the plant. The study was conducted to scrutinize the contaminants removal efficiency of the Murta plant in a lab-scale vertical subsurface flow constructed wetland (VSSFCW). Two CW columns were installed for the experiment: one kept planted (experimental) with the Murta plants and the another remained unplanted (control). Afterward a two months stabilization period, water samples were analyzed from the influent storage tank and both the experimental and control systems effluent at 24 h hydraulic retention time (HRT) for one month study period. The CWs were operated in the batch mode, for completing one cycle it run for one day, in keeping the flow 0.012m3/d and the hydraulic loading rate (HLR) 0.13 m3/d/m2. The results indicated higher reduction capability in the planted CW: 61.60 ± 2.85% Biochemical oxygen demand (BOD5), 53.98 ± 11.84% Chemical oxygen demand (COD), 70.25 ± 15.33% Nitrate (NO3-N), and 39.36 ± 30.85% Nitrite (NO2-N) reduction occurred in the column. Conversely, the unplanted CW reduced 43.31 ± 9.37% BOD5, 45.34 ± 8.88% COD, 9.92 ± 5.32 % NO3-N, and 15.87 ± 25.07% NO2-N. The study reports the reduction efficacy of the biochemical pollutants enhanced with the increase of the influent concentration. The average concentration of physical parameters of the influent, planted and unplanted CW was, respectively: 7.62±0.28, 6.8±0.16, 6.94±0.14 pH; 1107±140.50, 1199.03±57.48, 1050.75±96.18 μS/cm electrical conductivity (EC); 545.67±72.26, 533.51±84.12, 596.34±33.13 mg/L total dissolved solids (TDS); 0.55±0.07, 0.59±0.03, 0.52±0.02% salinity; 919.06±111.64, 835.27±39.53, 952.20±66.01 Ώ-cm resistivity; and 3.20±1.77, 5.15±1.00, 5.03±0.96 mg/L dissolved oxygen (DO). Therefore, 62% dissolved oxygen (DO) increased in the planted CW column than the influent sample water, whereas 59% DO enhance in the control. After all, the study suggests that S. dichotomus has significant organic reduction efficacy in the VSSFCW system, and could be regarded as an efficient CW plant.

Effects of high-strength landfill leachate effluent on stress-induced microalgae lipid production and post-treatment micropollutant degradation

This research investigates the effects of landfill leachate effluent concentrations from moving bed biofilm reactor (MBBR) on stress-induced Chlorella vulgaris and Scenedesmus armatus lipid production and post-treatment micropollutant degradation. The effluent concentrations were varied between 25%, 50%, 75%, and 100% (v/v). The landfill leachate influent was treated using two-stage moving bed biofilm reactor under 24 h and 18 h hydraulic retention time (HRT). The results indicated that the effluent concentration was positively correlated with the stress-induced microalgae lipid production in the post-treatment of residual micropollutants. C. vulgaris and S. armatus completely remove residual micropollutants in the effluent. The superoxide dismutase and peroxidase activity were positively correlated with the cellular lipid content. The lipid content of C. vulgaris and S. armatus cultivated in the 18 h HRT effluent were 31–51% and 51–64%, while those in the 24 h HRT effluent were 15–16% and 5–19%. The optimal condition of microalgae cultivation for the post-treatment of residual micropollutants was 50–75% (v/v) effluent concentrations under 18 h HRT, achieving the highest lipid production of 113–116 mg/L for C. vulgaris and 74–75 mg/L for S. armatus. Essentially, the MBBR landfill leachate effluent holds promising potential as a substrate for microalgae lipid production.

The microbial synergy and response mechanisms of hydrolysis-acidification combined microbial electrolysis cell system with stainless-steel cathode for textile-dyeing wastewater treatment

Microbial electrolysis cell (MEC) has been existing problems such as poor applicability to real wastewater and lack of cost-effective electrode materials in the practical application of refractory wastewater. A hydrolysis-acidification combined MEC system (HAR-MECs) with four inexpensive stainless-steel and conventional carbon cloth cathodes for the treatment of real textile-dyeing wastewater, which was fully evaluated the technical feasibility in terms of parameter optimization, spectral analysis, succession and cooperative/competition effect of microbial. Results showed that the optimum performance was achieved with a 12 h hydraulic retention time (HRT) and an applied voltage of 0.7 V in the HAR-MEC system with a 100 μm aperture stainless-steel mesh cathode (SSM-100 μm), and the associated optimum BOD5/COD improvement efficiency (74.75 ± 4.32 %) and current density (5.94 ± 0.03 A·m−2) were increased by 30.36 % and 22.36 % compared to a conventional carbon cloth cathode. The optimal system had effective removal of refractory organics and produced small molecules by electrical stimulation. The HAR segment could greatly alleviate the imbalance between electron donors and electron acceptors in the real refractory wastewater and reduce the treatment difficulty of the MEC segment, while the MEC system improved wastewater biodegradability, amplified the positive and specific interactions between degraders, fermenters and electroactive bacteria due to the substrate complexity. The SSM-100 μm-based system constructed by phylogenetic molecular ecological network (pMEN) exhibited moderate complexity and significantly strong positive correlation between electroactive bacteria and fermenters. It is highly feasible to use HAR-MEC with inexpensive stainless-steel cathode for textile-dyeing wastewater treatment.

Simultaneous removal of selenite and heavy metals from wastewater and their recovery as nanoparticles using an inverse fluidized bed bioreactor

Occurrence of selenium oxyanions and different heavy metals as co-pollutants in various waste streams is common from industries such as mining, coal burning, thermal power plants, petrochemical refinery, etc. Among the available technologies to treat such wastewater, biological removal using anaerobic microbes is one of the most advantageous. This study examined simultaneous removal and recovery of selenite and heavy metals using an inverse fluidized bed bioreactor (IFBR). The effect of commonly occurring heavy metals namely Zn, Cu and Cd on selenite removal was evaluated at 24 h hydraulic retention time (HRT). The maximum selenite removal of 93.9% was obtained in the absence of any heavy metals. The presence of heavy metals negatively impacted the selenite removal (45.8–85.3%), and the inhibitory effect due to Cu was the most significant among the three metals at 50 mg/L of influent concentration (47% lower). The heavy metal removal efficiency values were more than 70%, except in the case of Cd at 50 mg/L. The recovery values of selenium and heavy metals using the continuous bioreactor were in the range 45.1–73.9% and 59.2–69.8%, respectively, under different experimental conditions. Elemental selenium nanoparticles were formed inside the bioreactor due to selenite bioreduction and the nanoparticle size ranged from 50 to 300 nm. Furthermore, formation of small sized (<10 nm) metal selenide nanoparticles of the respective metals were detected during the bioreactor operation. Overall, this study clearly demonstrated the potential of the IFBR system for the removal of selenite and heavy metals from wastewater as well as their recovery as elemental selenium and metal selenide nanoparticles, respectively.

Enhanced biological nitrogen and phosphorus removal from sewage driven by fermented glycerol: comparative assessment between sequencing batch- and continuously fed-structured fixed bed reactor.

The nutrient biological removal from sewage, especially from anaerobic reactor effluents, still represents a major challenge in conventional sewage treatment plants. In this work, the nitrogen and phosphorus removal from anaerobic pre-treated domestic sewage in an up-flow anaerobic sludge blanket (UASB) reactor was assessed in a structured fixed bed reactor (SFBR) operated in a continuous and in a batch mode using polyurethane foam as material support for biomass and fermented glycerol as the exogenous carbon source. The SFBR was operated as a sequencing batch reactor with cycles of 90, 120, and 150min under anaerobic, oxic, and anoxic conditions, respectively, reaching average efficiencies for total nitrogen and phosphorus removal of 88% and 56%, respectively. Fermented glycerol was added during the non-aerated periods. Under continuous feeding, the SFBR was operated with aeration/non-aeration periods of 2/1 (h) and 3/1 (h), hydraulic retention time of 12h, and a recirculation ratio of 3. Without fermented glycerol addition, the maximum removal of total nitrogen (TN) reached 42%, while adding glycerol in the non-aerated period improved TN removal to 64.9% (2/1h) and 69.5% (3/1h). During continuous operation, no phosphorus removal was observed, which was released during the non-aerated period, remaining in the effluent. Optical microscopy analyses confirmed the presence of polyphosphate granules and of the phosphorus accumulating organisms in the reactor biofilm. It was concluded that the batch feeding method was determinant for phosphorus removal. The structured fixed bed reactor with polyurethane foam proved to be feasible in the removal of organic matter and nutrients remaining in the UASB reactor effluent.

Sequential biological and solar photocatalytic treatment system for greywater treatment.

In this study, sequencing batch reactor (SBR) using anaerobic/aerobic/anoxic process was coupled to a solar photocatalytic reactor (SPCR) for greywater treatment. The greywater effluent from SBR (operated at the optimal condition: 6.8 h hydraulic retention time (HRT), 0.7 Volumetric exchange ratio (VER) and 7.94 d solids retention time (SRT) with optimal corn cob adsorbent dosage (0.5 g/L)) was fed to the SPCR (operated at optimal conditions: pH - 3, H2O2 dosage - 1 g/L, catalyst dosage - 5 g/L). Chemical oxygen demand (COD) removal of 92.8±0.5% and ∼100% were achieved in SBR and SBR-SPCR, respectively. Similarly, total organic carbon (TOC) removal of 91±0.9% and ∼100% were observed in SBR and SBR-SPCR, respectively. After SBR treatment, average total nitrogen (TN) removal of 84% was found and this TN removal increased to 93% after combined SBR-SPCR treatment. The maximum PO43-_P reduction of 80±1.5% % was achieved with SBR-adsorption system. In addition, a maximum of 87±0.9% of net PO43-_P removal was reached after SBR-SPCR treatment. 58.9±2.3% BP (benzophenone-3) removal was obtained in the SBR while the integration of SBR and SPCR treatment was resulted in 100% BP removal. An effective anionic surfactant (AS) removal rate (80.1±2.2%) was observed in the SBR phase, which further improved to 94.9±1% at the end of 4 h SPCR treatment.

Co-substrates' influence on bioelectricity production in an azo dye-based microbial fuel cell

Co-substrates have been known to influence bioelectricity output during dye degradation. This preliminary research is focused on understanding the variations of bioelectricity output when co-substrates glucose and nitrogen sources were added along with Congo red azo dye in a double-chambered microbial fuel cell (MFC). A novel bacterial consortium capable of azo dye degradation was added as the inoculant to the double-chambered MFC. Differences in bioelectricity output were noted when glucose alone, ammonium nitrate and ammonium phosphate alone were added as co-substrates with Congo red dye. MFC with 25 mg L−1 ammonium nitrate peaked 0.032V and 0.003A open circuit (OC) output after 8 h hydraulic retention time (HRT). This was followed by observing effects of glucose alone and glucose combined with nitrogen sources over 8 h. Peak voltage and current of 0.11V and 0.012A, respectively were achieved at 3 h HRT by experimental model with glucose alone as co-substrate.

Electrochemical treatment of two health-care wastewaters – A comparative study

ABSTRACT Organics removal from health-care wastewaters (HCWWs) is of prime concern worldwide. Water reclamation along with treatment using electrochemical technique was achieved in the present research. Partial mineralization was achieved using two-dimensional (2D) iron electrodes for cell voltages of 3, 6, 9, 12, and 15 V for an electrolysis time (ET) of 60 min for a fixed SA/V specific electrode area to a volume of 40 m2m−3. The maximum COD and TDS removal of 88.4% and 58.44% was obtained for Government HCWW compared to private HCWW of 79.5% and 50.6%, respectively, at 12 V for 60 min ET. ECC experiments were also carried out for discrete ETs for optimized 12 V cell voltage. Along with COD and TDS, other quality parameters were also analyzed after 1 h hydraulic retention time (HRT). After ECC, total alkalinity, chloride, and total solids significantly reduced from their initial values. ECC showed good disinfection potential by lysing pathogens in HCWWs at 45–60 min ET. Post ECC slurry for both HCWWs showed good filterability. The current efficiency (CE) was 200–220% and specific energy consumption (SEC) was 25–80 kWh/kg of COD removed for 45–60 min ET. Water reclamation of 80–85% was possible after settling, followed by filterability of treated supernatant for both HCWWs.