Recent research in wastewater treatment demonstrates that activated sludge plants can be operated more efficiently in terms of energy and carbon utilization without the need for new infrastructure through the implementation of low dissolved oxygen (DO) operation. The aim of this study was to understand how microbial communities adapt to long-term low DO operations and the implications for nitrification. This study synthesized findings from bench-scale and full-scale experiments to assess the impact of low DO operation on nitrification rates, microbial community structure, and nitrous oxide (N2O) generation. Long-term exposure to low DO conditions led to a shift in the nitrifier community structure, favoring comammox bacteria (CMX) and, in some cases, ammonia-oxidizing archaea (AOA) over canonical ammonia-oxidizing and nitrite-oxidizing bacteria (AOB, NOB). In conventional high-DO systems, the ratio of nitrate production rate to ammonia removal rate is approximately 0.78, reflecting the lower growth rate of NOB compared to AOB. However, in the low DO facilities studied, this ratio approached 1.0, indicating that nearly all ammonia removed was directly converted to nitrate. This finding strongly supports the dominance of CMX which can perform complete ammonia oxidation in a single organism. The correlation between increased CMX abundance and increased nitrate production rates was consistent across facilities operating at different DO levels. These adapted communities demonstrated higher oxygen affinity compared to AOB and NOB from plants operated at high DO concentrations. Long-term exposure of biomass to low DO concentration may have resulted in a decrease in N2O emissions since there is a low relative abundance of AOB and NOB, limiting N2O production via the hydroxylamine oxidation pathway and nitrifier denitrification by AOB.

Comparative growth rate measurement of 51 lysozyme seeded crystals at various supersaturations under microgravity and in normal gravity were successfully conducted by ex-situ method in a Russian Foton-M3 recovery satellite. Growth rate of crystals both in space and on the Earth were calculated by measuring the thickness of each growth zone that was caused by the change of gravity level. It is surprising to find that growth rate under microgravity was the same as that in normal gravity or, unexpectedly, even larger by more than 20 %. The experiment was conducted in the satellite in 12 days under microgravity after 6 days transportation on the ground from Nijmegen, the Netherlands, to Baikonur, Russia. 51 growth cells were kept at 20celcius after the protein solutions and the seeds were sealed. The trace of movement of 2D macro-steps on the (110) face was visualized after the flight by laser confocal microscopy. These steps were buried inside the crystals, 0-140 mu m deep from the surface and so they were grown in space. The observed elongated sharp 2D steps implies that the effect of impurity was considerably reduced in space condition, compared with the rounded shape of 2D steps formed with more impurities in normal gravity. The increase in growth rate in space could be concluded due to the reduction of impurities on the surface of crystals. Several space grown crystals were examined by synchrotron X-ray topography at KEK in Tsukuba after optical observations were completed. The change of lattice perfection due to the change from normal G to mu G was investigated using local rocking curve analysis (peak position, intensity, full width at half maximum) as well as X-ray topography. Clear increase of diffraction and thus better perfection were observed when the gravity changed from normal G to mu G condition. However, it should be noted that perfection of the space grown crystal reached the value of the best portion of the seed crystal that was carefully prepared on the Earth. Based on these data, increased growth rate in space is conclude to be due to the reduction of impurity effects at the surface of the crystals. Better perfection might additionally increase the growth rate.

This study presents results from the City of St. Petersburg's (Florida) Southwest Water Reclamation Facility. This high-rate BNR plant (SRT ~ 5 days; HRT < 8 hr) achieves combined bioP and shortcut simultaneous nitrification and denitrification (SND) via nitrite in a simple BNR configuration-an anaerobic-aerobic (A/O) process without mixed liquor recycle and a 25% unaerated fraction. N removal to low effluent and nitrate and nitrite ( NO 3 - + NO 2 - ) concentrations occurs mainly via SND by operating the aerated zone at low DO, but still achieving near-complete ammonium ( NH 4 + ) removal. Despite the low DO operation, very good bioP performance is achieved. Full-scale performance data and detailed bench-scale testing were conducted to assess the nitrogen and phosphorus removal at low DO conditions. Full-scale results showed that the plant achieves effluent total inorganic nitrogen (TIN) and total phosphorus (TP) concentrations of approximately 2.0 mgN/L and 0.5 mgP/L, respectively, at an average influent C:N ratio of 7:1 mgCOD:mgN. PRACTITIONER POINTS: Simple anaerobic-aerobic (A/O) process demonstrated combined N and P removal Ammonia oxidation was not hampered by low DO (<0.5 mg/L) operation Low DO (<0.5 mg/L) operation sustained SND via nitrite pathway in a high-rate process (HRT < 6 hr) P uptake was demonstrated at low DO which counters to the widely held understanding that high DO (>1.5 mg/L) is necessary Heterotrophic consumption of nitrite at low DO was the key to the out-selection of nitrite-oxidizing bacteria.

Quaternary ammonium compounds (QACs) are surface-active organic compounds common in industrial cleaner formulations widely used in various sanitation applications. While acting as effective pathogenic biocides, QACs lack selective toxicity and often have poor target specificity. As a result, adverse effects on biological processes and thus the performance of biological nutrient removal (BNR) systems may be encountered when QACs enter wastewater treatment plants (WWTPs). Because of these impacts, there is motivation to screen wastewater influents for QACs and for process engineers to consider the inhibition effects of QACs on process evaluation and design of BNR plants. This paper introduces a mathematical model to describe the fate of QACs in a WWTP via biodegradation and bio-adsorption, and the inhibitory effect of QACs on nitrifiers and ordinary heterotrophic organisms. The model was incorporated as an add-on model in BioWin 5.3 and simulations of experimental systems were used for comparison of model results to measured data reported in the literature. The model was found to accurately predict the bulk phase concentration of QAC and the inhibition of nitrification with QAC concentrations ≥2 mg/L. This work provides a preliminary framework for simulation of BNR plants receiving inhibitory substances in the influent.

High-rate biological wastewater treatment processes for carbon recovery are able to improve the energy balance and carbon footprint of water resource recovery facilities. Combination of a high-rate moving bed biofilm reactor (HR-MBBR) with a rapid flotation (HR-DAF), as a replacement for the ‘A stage’ of the A-B process, can achieve this objective. The main goal of this study was to maximize the capture of biodegradable particulate matter from an HR-MBBR effluent by an HR-DAF. A pilot-scale HR-DAF process was operated downstream of an HR-MBBR treating screened municipal wastewater. The particulate biodegradable matter recovery was evaluated by determining the total suspended solids (TSS) removal efficiency. TSS recovery in experiments without chemicals at low surface loading rates (<15 m/h) and high recycle ratio (>25%) was 94 ± 1%. By using a tannin-based polymer, the solids capture efficiency of the HR-DAF was slightly improved with TSS recovery reaching 96 ± 1% at a high SLR (at least 22 m/h) and low recycle ratio (14%). The anaerobic biodegradability of the tannin tested was determined to be 17%. The HR-DAF process downstream of an HR-MBBR gave a very good particulate matter recovery that offers a promising alternative to the A-B process for carbon recovery.

The main objective of this study was to develop an innovative process to maximize the bio-transformation of colloidal and soluble biodegradable matter (CSB) into particulate matter (XB) for energy recovery via methane production. Two configurations were studied: (1) high-rate moving bed bioreactor (HR-MBBR) and (2) inoculum-chemostat (IC) system consisting of a very HR-MBBR inoculating a continuous flow stirred-tank reactor. The effect of hydraulic retention time (HRT), specific organic loading rate (SOLR), and dissolved oxygen (DO) level were determined using real wastewater at pilot scale. Results showed that in the HR-MBBR process, a very high CSB bio-transformation efficiency (90%) was obtained in a wide range of SOLRs (2.0 to 5.5 g CSB m−2 d−1) corresponding to an optimum HRT of 36 minutes. The IC process reached a maximum CSB bio-transformation efficiency of 77%, at SOLRs ranging from 22 to 30 g CSB m−2 d−1 at an HRT of 3.7 hours. The DO concentration in the HR-MBBR influenced the CSB bio-transformation ratio, while the HRT and the SOLR were the dominant factors influencing this ratio in the IC process. Based on these results, the IC process could be an interesting alternative to high-rate systems towards obtaining energy positive/efficient from water resource recovery facilities.

An important part of biological treatment system design is quantifying the sludge production and the nutrient removal capacity. Influent wastewater COD fractionation, biomass growth and endogenous respiration directly impacts the composition of the mixed liquor solids in activated sludge systems. The objectives of this project were to determine the model kinetic and stoichiometric parameters associated with activated sludge production and the nutrient content (N and P) of unbiodegradable organic matter components. A complete sludge retention experiment was conducted over 70 days in a pilot-scale membrane bioreactor fed with a real municipal wastewater, and operated with alternating growth and famine periods. Experimental results were simulated and compared using the default values from two well-accepted model parameter sets. The General ASDM parameter set was found to better fit the experimental data than the Metcalf and Eddy parameter set, mainly to characterize endogenous respiration and the heterotrophic biomass concentration. An influent unbiodegradable organic particulate fraction (f(XU), (Inf)) value of 0.16 g COD/g COD was determined by calibration of the accumulated sludge total COD, suspended solids and heterotrophic biomass concentrations. The nutrient content of the accumulated endogenous residue (XE) and influent unbiodegradable organic particulate (X-U, (Inf)) components were calibrated to 0.030 and 0.100 g N/g COD and 0.035 and 0.008 g P/g COD, respectively. These values are in the range of those reported in the literature except for the high P content found in the endogenous residue, possibly due to the presence of coagulants added for P removal in the accumulated sludge. These results were consistent under the wide range of dynamic conditions tested and could improve model prediction of sludge production and composition.

High-rate wastewater processes are receiving a renewed interest to obtain energy positive/efficient water resource recovery facilities. An innovative treatment train combining a high-rate moving bed biofilm reactor (HR-MBBR) with an enhanced flotation process was studied. The two objectives of this work were 1) to maximize the conversion of soluble organics to particulate matter in an HR-MBBR and 2) to maximize the particulate matter recovery from the HR-MBBR effluent by green chemicals to enhance biogas production by anaerobic digestion. To achieve these objectives, lab-scale MBBRs fed with synthetic soluble wastewater were operated at organic loading rates (OLRs) between 4 and 34 kg COD m(-3) reactor d(-1) corresponding to hydraulic retention times (HRTs) between 6 and 54 min.Colloidal and soluble chemical oxygen demand (COD) removal efficiency in the HR-MBBR increased with HRT to reach a plateau of 85% at an HRT longer than 27 min. Carrier clogging observed at an OLR higher than 16 kg COD m(-3) d(-1) (HRT < 13 min) resulted in about 23% loss in colloidal and soluble COD removal efficiency. Thus, the recommended parameters were between 22 and 37 min and between 6 and 10 kg COD m(-3) d(-1) for the HRT and the OLR, respectively, to maximize the conversion of soluble organics to particulate matter.Total suspended solids (TSS) recovery of 58-85% and 90-97% were achieved by enhanced flotation using green and unbiodegradable chemicals, respectively, corresponding to a TSS effluent concentration below 14 and 7 mg TSS/L. Among the synthetic polymers tested, a high molecular weight and low charge density cationic polyacrylamide was found to give the best results with less than 2 mg TSS/L in the clarified effluent (97% TSS recovery). Green chemicals, although performing slightly less for solids separation than unbiodegradable chemicals, achieved a mean TSS concentration of 10 +/- 3 mg/L in the clarified effluent. (C) 2016 Elsevier Ltd. All rights reserved.

ABSTRACT: Reducing excess sludge production is increasingly attractive as a result of rising costs and constraints with respect to sludge treatment and disposal. A technology in which the mechanisms remain not well understood is the Cannibal process, for which very low sludge yields have been reported. The objective of this work was to use modeling as a means to characterize excess sludge production at a full‐scale Cannibal facility by providing a long sludge retention time and removing trash and grit by physical processes. The facility was characterized by using its historical data, from discussion with the staff and by conducting a sampling campaign to prepare a solids inventory and an overall mass balance. At the evaluated sludge retention time of 400 days, the sum of the daily loss of suspended solids to the effluent and of the waste activated sludge solids contributed approximately equally to the sum of solids that are wasted daily as trash and grit from the solids separation module. The overall sludge production was estimated to be 0.14 g total suspended solids produced/g chemical oxygen demand removed. The essential functions of the Cannibal process for the reduction of sludge production appear to be to remove trash and grit from the sludge by physical processes of microscreening and hydrocycloning, respectively, and to provide a long sludge retention time, which allows the slow degradation of the “unbiodegradable” influent particulate organics (XU,Inf) and the endogenous residue (XE). The high energy demand of 1.6 kWh/m3 of treated wastewater at the studied facility limits the niche of the Cannibal process to small‐ to medium‐sized facilities in which sludge disposal costs are high but electricity costs are low.