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Minimization of excess sludge produced by wastewater treatment plants has become a topical theme nowadays. One of the most used approaches to achieve this aim is the anaerobic side-stream reactor (ASSR) process. This is considered affected by the hydraulic retention time (HRT) of the anaerobic reactor, the anaerobic sludge loading rate (ASLR) and the sludge interchange ratio (SIR), although, studies available in the literature did not reflect a clear relationship with the sludge minimization yields. To overcome this, a novel parameter namely anaerobic exposure time (AET) was defined and related to reduction of the observed yield coefficient (Y obs ) in a lab-scale plant implementing the ASSR process. Furthermore, the AET was validated by performing a detailed and thorough review of previous literature. Excess sludge production was successfully reduced (10-60 %) with the increase of the AET (7.9-13 h/d), although maintaining the same HRT in the ASSR and a constant sludge interchange ratio (SIR) (100 %). A strong correlation (Pearson = 0.763) was found between the AET, and the Y obs reduction reported in previous studies, also indicating a linear relationship (R 2 = 0.92) between these parameters. Contrarily, the correlation between the Y obs with the ASLR and the ASSR-HRT resulted moderate (Pearson = 0.186) or weak (Pearson=-0.346), respectively. Overall, while operating at low AET (< 6 h), maintenance and uncoupling metabolism were found the main sludge reduction mechanisms. Increasing the AET (>8 h) favoured the occurrence of extracellular polymeric substances (EPS) hydrolysis and endogenous decay mechanisms, which improved excess sludge reduction. To conclude, the AET could be considered a reliable parameter to be used for design or control purposes for the ASSR-based process., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Iron sulphides, mainly in the form of mackinawite (FeS), pyrrhotite (Fe 1-x S, x = 0-0.125) and pyrite (FeS 2 ), are the most abundant sulphide minerals and can be oxidized under anoxic and circumneutral pH conditions by chemoautotrophic denitrifying bacteria to reduce nitrate to N 2 . Iron sulphides mediated autotrophic denitrification (ISAD) represents an important natural attenuation process of nitrate pollution and plays a pivotal role in linking nitrogen, sulphur and iron cycles in a variety of anoxic environments. Recently, it has emerged as a promising bioprocess for nutrient removal from various organic-deficient water and wastewater, due to its specific advantages including high denitrification capacity, simultaneous nitrogen and phosphorus removal, self-buffering properties, and fewer by-products generation (sulphate, waste sludge, N 2 O, NH 4 + , etc.). This paper provides a critical overview of fundamental and engineering aspects of ISAD, including the theoretical knowledge (biochemistry, and microbial diversity), its natural occurrence and engineering applications. Its potential and limitations are elucidated by summarizing the key influencing factors including availability of iron sulphides, low denitrification rates, sulphate emission and leaching heavy metals. This review also put forward two key questions in the mechanism of anoxic iron sulphides oxidation, i.e. dissolution of iron sulphides and direct substrates for denitrifiers. Finally, its prospects for future sustainable wastewater treatment are highlighted. An iron sulphides-based biotechnology towards next-generation wastewater treatment (NEO-GREEN) is proposed, which can potentially harness bioenergy in wastewater, incorporate resources (P and Fe) recovery, achieve simultaneous nutrient and emerging contaminants removal, and minimize waste sludge production., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Recently, the Sulfate reduction Autotrophic denitrification Nitrification Integrated (SANI(®)) process was developed for the removal of organics and nitrogen with sludge minimization in the treatment of saline sewage (with a Sulfate-to-COD ratio > 0.5 mg SO4(2-)-S/mg COD) generated from seawater used for toilet flushing or salt water intrusion. Previously investigated in lab- and pilot-scale, this process has now been scaled up to a 800-1000 m(3)/d full-scale demonstration plant. In this paper, the design and operating parameters of the SANI demo plant built in Hong Kong are analyzed. After a 4-month start-up period, a stable sulfur cycle-based biological nitrogen removal system having a hydraulic retention time (HRT) of 12.5 h was developed, thereby reducing the amount of space needed by 30-40% compared with conventional activated sludge (CAS) plants in Hong Kong. The demo plant satisfactorily met the local effluent discharge limits during both the summer and winter periods. In winter (sewage temperature of 21 ± 1 °C), the maximum volumetric loading rates for organic conversion, nitrification, and denitrification were 2 kg COD/(m(3)·d), 0.39 kg N/(m(3)·d), and 0.35 kg N/(m(3)·d), respectively. The biological sludge production rate of SANI process was 0.35 ± 0.08 g TSSproduced/g BOD5 (or 0.19 ± 0.05 g TSS/g COD), which is 60-70% lower than that of the CAS process in Hong Kong. While further process optimization is possible, this study demonstrates the SANI process can be potentially implemented for the treatment of saline sewage., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The activated sludge process is the most widely used treatment method for municipal wastewater. However, the excessive amount of biomass generated during the process is a major drawback. Earlier studies using the activated sludge process running in a biomass fasting and feasting mode demonstrated both nutrient removal and a minimization of biomass production. However, these studies were conducted using synthetic wastewater. In this study, we report findings from a lab-scale sludge-minimizing biological nutrient removing (BNR) reactor when its operation was changed from synthetic to real wastewater (primary effluent). Two lab-scale sequencing batch reactors, one in sludge minimization mode (hereafter called modified-SBR), and the other in conventional activated sludge mode (referred as control-SBR), were operated for more than 300 days. Both reactors were started and operated with synthetic feed. Gradually the feed to both reactors was changed to 100% primary effluent collected from a local full-scale wastewater treatment plant. Irrespective of the feed composition, more than 98% NH3-N removal was recorded in both SBRs. However, while 89% of the total dissolved phosphorus was removed from the 100% synthetic feed, only 80% of the total dissolved phosphorus was removed from the 100% primary effluent in both SBRs. The overall observed sludge reduction in the modified-SBR as compared to the control-SBR also decreased from 65% to 39% when the feed was changed from 100% synthetic to 100% primary effluent. The specific oxygen uptake rate for the modified-SBR was 80% higher than that for the control-SBR when the SBRs were fed with primary effluent wastewater. The modified-SBR showed a greater diversity of ammonia-oxidizing bacteria (AOBs) with synthetic wastewater as well as during the transition period than the control-SBR. Yet when the reactors were running on 100% real wastewater, only Nitrosomonas europaea/eutropha were identified in both SBRs. The nitrite-oxidizing bacterial community and the polyphosphate accumulating organisms (PAOs) responded in a similar way in both SBRs., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

In the present work we studied the thermophilic biological treatability of high strength liquid wastes from a pharmaceutical industry (rich in organic matter - COD: Chemical Oxygen Demand, nutrients and salinity). Different mixtures (with concentrations of COD, phosphorus and chloride up to 57,000 mg L(-1), 2000 mg L(-1) and 9000 mg L(-1), respectively) were tested. The pilot plant used in this work was designed and built with dimensions comparable to a semi-industrial unit. The results are therefore representative for full-scale applications. During four months of experimentation, the pilot plant (TAMR - Thermophilic Aerobic Membrane Reactor) was operated at 49 ± 1 °C and the organic loading rate was 1.5-5.5 kgCOD m(-3) d(-1) with a hydraulic retention time of 5-10 days. Main results are the following: a) extremely high COD removal rate (up to 98%); b) very low sludge production (∼0.016 kgVSS produced kgCOD removed(-1)); c) suitability as a pre-treatment to a conventional (e.g. activated sludge) biological treatment (the studied pharmaceutical industrial wastewaters are discharged into the sewer system for final polishing in a centralized municipal wastewater treatment plant) and d) high phosphorus removal (up to 99%)., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Solids reduction in activated sludge processes (ASP) at source using process manipulation has been researched widely over the last two-decades. However, the absence of nutrient removal component, lack of understanding on the organic carbon, and limited information on key microbial community in solids minimizing ASP preclude the widespread acceptance of sludge minimizing processes. In this manuscript, we report simultaneous solids reduction through anaerobiosis along with nitrogen and phosphorus removals. The manuscript also reports carbon mass balance using stable isotope of carbon, microbial ecology of nitrifiers and polyphosphate accumulating organisms (PAOs). Two laboratory scale reactors were operated in anaerobic-aerobic-anoxic (A(2)O) mode. One reactor was run in the standard mode (hereafter called the control-SBR) simulating conventional A(2)O type of activated sludge process and the second reactor was run in the sludge minimizing mode (called the modified-SBR). Unlike other research efforts where the sludge minimizing reactor was maintained at nearly infinite solids retention time (SRT). To sustain the efficient nutrient removal, the modified-SBR in this research was operated at a very small solids yield rather than at infinite SRT. Both reactors showed consistent NH3-N, phosphorus and COD removals over a period of 263 days. Both reactors also showed active denitrification during the anoxic phase even if there was no organic carbon source available during this phase, suggesting the presence of denitrifying PAOs (DNPAOs). The observed solids yield in the modified-SBR was 60% less than the observed solids yield in the control-SBR. Specific oxygen uptake rate (SOUR) for the modified-SBR was almost 44% more than the control-SBR under identical feeding conditions, but was nearly the same for both reactors under fasting conditions. The modified-SBR showed greater diversity of ammonia oxidizing bacteria and PAOs compared to the control-SBR. The diversity of PAOs in the modified-SBR was even more interesting in which case novel clades of Candidatus Accumulibacter phosphatis (CAP), an uncultured but widely found PAOs, were found., (Copyright © 2014 Elsevier Ltd. All rights reserved.)