Search

This article discussed the effect of the main operating parameter involved in the operation of algal–bacterial granular sludge (ABGS) systems as promising biological processes for wastewater treatment. The focus was on the operational ranges reported in the literature capable of achieving better granule properties, good stability and high removal capacities. This review identified that hydraulic retention time (HRT), light intensity (LI) and light/dark periods were the most influential operating factors on the formation, stability, settleability and organic pollutant removal efficiency of ABGS. The discussion argued that ABGS systems enhance industrial and domestic wastewater treatment due to additional advantages that provide the symbiotic interactions to process performance, maintaining lesser operating costs concerning aerobic granular sludges (AGS) and microalgae consortia. This review will improve the understanding of the operation of ABGS systems and thus further expand possible operating combinations that help to enhance microbial interactions, microalgae growth and external aeration self‐sufficiency in further research with a focus on its scaling up. [ABSTRACT FROM AUTHOR]

The digestion efficiency of liquid industrial wastes increases when using bioreactors colonized by microbial biofilms. High concentrations of proteins derived from the fish processing industry lead to the production of ammonia, which inhibits methane production. Two bioreactors were constructed to compare methanogenic activity: one enriched with mMPA (methylaminotrofic methane production archaea) consortia (control bioreactor), and the second with NH3 tolerant consortia (treatment bioreactor). Ammonia tolerant activity was assessed by applying an ammonia shock (755 mg NH3/L). Methane production, consumption of total organic carbon (TOC) and the taxonomic composition of bacteria and archaea was evaluated using 16S rDNA in the acclimatization, ammonia shock, and recovery phases.The ammonia shock significantly affected both methane production and the consumption of TOC in the control reactor (p < 0.05) and taxonomical composition of the microbial consortia (OTU). These values remained constant in the treatment reactor. The analysis of biofilm composition showed a predominance of Methanosarcinaceae (Methanomethylovorans sp., and probably two different species of Methanosarcina sp.) in bioreactors. These results demonstrate that using acclimated biofilms enriched with ammonia tolerant methanogens control the inhibitory effect of ammonia on methanogenesis. [ABSTRACT FROM AUTHOR]

The internal recirculation plays an important role on the different biological processes of wastewater treatment plants because it has a great influence on the concentration of pollutants, especially nutrients. Usually, the internal recirculation flow rate is kept fixed or manipulated by control techniques to maintain a fixed nitrate set-point in the last anoxic tank. This work proposes a new control strategy to manipulate the internal recirculation flow rate by applying a fuzzy controller. The proposed controller takes into account the effects of the internal recirculation flow rate on the inlet of the biological treatment and on the denitrification and nitrification processes with the aim of reducing violations of legally established limits of nitrogen and ammonia and also reducing operational costs. The proposed fuzzy controller is tested by simulation with the internationally known benchmark simulation model no. 2. The objective is to apply the proposed fuzzy controller in any control strategy, only replacing the manipulation of the internal recirculation flow rate, to improve the plant operation.Therefore, it has been implemented in five operation strategies from the literature, replacing their original internal recirculation flow rate control, and simulation results are compared with those of the original strategies. Results show improvements with the application of the proposed fuzzy controller of between 2.25 and 57.94% in reduction of total nitrogen limit violations, between 55.22 and 79.69% in reduction of ammonia limit violations and between 0.84 and 38.06% in cost reduction of pumping energy. • New regulation of the internal recirculation flow rate in wastewater treatments. • Fuzzy logic is based on analysis of the internal recirculation effects. • The proposed fuzzy controller can be applied in any operation strategy. • A comparison with usual regulations have been carried out. • Improvements of effluent quality and operational costs are achieved. [ABSTRACT FROM AUTHOR]

Copyright of Environmental Science & Technology (10036504) is the property of Editorial Board of Environmental Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, we show that the combination of a photocatalytic process (as a pretreatment step) combined with the conventional biological treatment of wastewaters can improve the process and achieve satisfactory efficiency. In this context, Reactive Green 12 (RG-12) solutions were photocatalytically pretreated using TiO2-impregnated polyester as supported catalyst under UV light in batch reactor. Photocatalysis as pretreatment (during 4 and 8 h of irradiation) was combined with 7 days of aerobic biological treatment using activated sludge. As first assays, respiratory tests revealed that the removal of RG-12 was improved by 5.4% and 11.7% for the solutions that were irradiated for 4 and 8 h in the presence of TiO2, respectively. However, 34.5% and 19% of dye solution was discolored after 7 days of biological treatment for the pretreated solutions during 4 and 8 h of UV light exposure, respectively. The discoloration efficiency obtained by the combined processes achieved 59.6% and 74.9% for the samples under photocatalysis during 4 and 8 h, respectively. A significant decrease in chemical oxygen demand (COD) of about 74.9% was achieved after photocatalysis/biodegradation processes. In addition, a decrease in the phytotoxicity was obtained as followed by the germination index (GI) values of cress seeds that increased from 46.2 to 88.7% after 8 h of photocatalysis and then to 92.8% after further 7 days of biological treatment. [ABSTRACT FROM AUTHOR]

• Mechanisms of quorum sensing (QS) regulating EPS synthesis are elucidated. • Effects of QS on EPS synthesis in mixed microbial systems are reviewed. • Applications of QS-regulated EPS in wastewater microbial systems are discussed. • Research and development directions of QS regulation EPS are summarized. Extracellular polymeric substances (EPS) regulated by quorum sensing (QS) could directly mediate adhesion between microorganisms and form tight microbial aggregates. Besides, EPS have redox properties, which can facilitate electron transfer for promoting electroactive bacteria. Currently, the applications research on improving wastewater biological treatment performance based on QS regulated EPS have been widely reported, but reviews on the level of QS regulated EPS to enhance EPS function in microbial systems are still lacking. This work proposes the potential mechanisms of EPS synthesis by QS regulation from the viewpoint of material metabolism and energy metabolism, and summarizes the effects of QS on EPS synthesis. By synthesizing the role of QS in EPS regulation, we further point out the applications of QS-regulated EPS in wastewater biological treatment, which involve a series of aspects such as strengthening microbial colonization, mitigating membrane biofouling, improving the shock resistance of microbial metabolic systems, and strengthening the electron transfer capacity of microbial metabolic systems. According to this comprehensive review, future research on QS-regulated EPS should focus on the exploration of the micro-mechanisms, and economic regulation strategies for QS-regulated EPS should be developed, while the stability of QS-regulated EPS in long-term production experimental research should be further demonstrated. [Display omitted] [ABSTRACT FROM AUTHOR]

A great deal of efforts has been put into studying the influence of the external macroenvironment for activated sludge to survive on microbial community succession, while granular internal spatial microenvironment should be given equal attention, because it is more directly involved in the information exchange and material transfer among microorganisms. This study systematically investigated the effects of granular microenvironment on spatial colonization and composition of sludge's core functional flora, and the corresponding difference of biological treatment performance. High content of extracellular-proteins (67.53 mg/gVSS) or extracellular-polysaccharide (65.02 mg/gVSS) stimulated the microbial flocculation and aggregation of 0.5–1.5 mm granules (GS) or 1.5–3.0 mm granules (GM), respectively, which was resulted from excellent cell hydrophobicity (59.26%) or viscosity (3.47 mPa s), therefore, constituted relatively dense porous frame. More hollow space existed in 3.0–5.0 mm granules (GL), which formed loose skeleton with 0.213 mL/g of total pore volume and 17.21 nm of average pore size. Combining scanning electron microscope images and fluorescent in-situ hybridization based microbiological analysis, aerobic nitrifiers were observed to wrap or surround anaerobic bacteria, or facultative/anaerobic bacteria were self-encapsulated, which created granule's unique microenvironment with alternating aerobic and anaerobic zones. GS has the most rich organic matter degrading bacteria and anaerobic heterotrophic denitrifiers, while GM and GL presented the greatest relative abundance of facultative and aerobic denitrifiers, respectively. The activity of dehydrogenase and nitrogen invertase of GM showed be 1.32–3.09 times higher than those of GS and GL, contributing to its higher carbon and nitrogen removal. These findings highlight the importance of granular microenvironment to adaptive regulation of activated sludge's core functional flora and corresponding pollutant removal performance. [Display omitted] • Granular internal spatial microenvironment characteristics was analyzed in detail. • Functional flora and granular microenvironment are subject to two-way regulation. • 0.5–1.5 mm granules enriched the most organic degradation bacteria. • 3.0–5.0 mm granules have lots of hollow spaces and abundant aerobic denitrifiers. • 1.5–3.0 mm granules showed the greatest key biological enzyme activity. [ABSTRACT FROM AUTHOR]

• AGS-MBR greatly lowered fouling rate in comparison with that of the conventional MBR. • A new scouring model was developed to explain the AGS scouring mechanism. • The AGS scouring stress is proportional to the total amount of AGS on the membrane. • A contribution quantification model was built to evaluate fouling mitigation factors. • AGS scouring had a contribution rate of 39.97% for membrane fouling mitigation. Aerobic granular sludge (AGS) has been proven to have a low fouling potential in membrane bioreactor (MBR). Nevertheless, AGS scouring effect on mitigating membrane fouling remains poorly investigated. The main objective of this study is to examine AGS-MBR performance, to reveal the AGS scouring mechanism and quantify its contribution rate to membrane fouling mitigation, from the views of theory and experiment. Above all, AGS-MBR exhibited a low fouling rate ((transmembrane pressure (TMP) kept below 20 kPa) without membrane cleaning and a higher removal of organics and nutrients than conventional MBR during 80 days' sludge granulation process. Then, flocculent sludge (FS) with various AGS ratios was applied to simulate the sludge granulation phase. When AGS ratio increased from 0% to 100%, the permeate flux gradually elevated from 40.0 L m −2 h −1 to 92.9 L m −2 h −1, and fouling resistance decreased from 9.0 × 10−12 m −1 to 3.9 × 10−12 m −1 benefiting from the loose structure and high porosity of AGS fouling layer. Meanwhile, the scouring effect produced by AGS on the membrane fouling mitigation was investigated. Based on the momentum conservation, a new hydrodynamic model was developed to explain the scouring mechanism of AGS. The scouring stress, proportional to the total amount of AGS depositing on the membrane surface, effectively reinforced the collision between AGS and FS, and reduced their deposition on the membrane surface by friction with the membrane; thus it was further conducive to membrane fouling mitigation. Moreover, a novel contribution quantification model was proposed for analyzing the contribution rate of AGS scouring effect to mitigate membrane fouling. AGS scouring possessed a significant contribution rate (39.9%) for fouling mitigation, compared with AGS structure (50.3%) and hydraulic stress (9.7%). In final, this study provides an in-depth understanding to mitigate the MBR membrane fouling by the unique advantages of sludge granulation. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Disposed pharmaceuticals constitute a significant threat to the environment due to the high consumption of drugs and inefficient treatment of wastewater. In this paper, we first described the efficient removal of a series of antidepressants and immunosuppressant from a cultivation medium carried out by white-rot fungus, Pleurotus ostreatus. We determined the removal efficiency of pharmaceuticals and the activity of fungal ligninolytic enzymes over time, as well as the toxicity of pre- and post-cultivation medium to Spirostomum ambiguum. We showed that P. ostreatus can remove from the model medium most of the pharmaceuticals studied, including clomipramine, mianserin, paroxetine, sertraline, and mycophenolic acid. Pharmaceuticals containing phenolic or benzene moieties, likewise in the natural monolignols, were removed in a high efficiency within a short time. The activity of the fungal ligninolytic enzymes, laccase, and lignin peroxidase, in the cultivation medium, was three times higher in the presence of the pharmaceuticals, which justifies their contribution to the degradation. The post-cultivation medium showed lower toxicity than pre-cultivation medium and toxic units were 7- and 2-fold lower for the sublethal and lethal response, respectively. Over twenty metabolites we detected resulted mostly from oxygenation or demethylation of parent pharmaceuticals. The biological treatment we developed using P. ostreatus -based system should be convenient and effective in mycoremediation of environmental wastewater polluted with emerging contaminants including monolignol-like antidepressants and immunosuppressant. • Pleurotus ostreatus removes well monolignol-like antidepressants from cultivation. • P. ostreatus degradation of antidepressants reduces toxicity towards S. ambiguum. • Oxidation and demethylation are main metabolic transformations of antidepressants. • Mycoremediation might be used to decontaminate environment from antidepressants. [ABSTRACT FROM AUTHOR]