Phosphate removal in agro-industry: pilot- and full-scale operational considerations of struvite crystallization

Pilot-scale struvite crystallisation tests using anaerobic effluent from potato processing industries were performed at three different plants. Two plants (P1 & P2) showed high phosphate removal efficiencies, 89 + 3% and 75 + 8%, resulting in final effluent levels of 12 + 3 mg PO4/3- -P/L and 11 + 3 mg PO4/3- -P/L, respectively. In contrast, poor phosphate removal (19 + 8%) was obtained at the third location (P3). A noticeable difference in the influent Ca2+/PO4/3- -P molar ratio was observed between the test sites, ranging from 0.27 + 0.08 (P1), 0.62 + 0.18 (P2) and 0.41 + 0.04 (P3). A negative effect on struvite formation occurred when a Ca2+/PO4/3- -P molar ratio of 1.25 + 0.11 was obtained after initial pH increase in the stripper at P3. A full-scale struvite plant treating 90–110 m3/h of anaerobic effluent from a diary industry also showed Ca2+ interference. Initially in this plant, influent phosphate levels ranging from 40 to 45 mg PO4/3- -P/L were decreased to below 10 mg PO4/3- -P/L, but no struvite was produced. A shift in Ca2+/PO4/3- -P molar ratio from 2.69 to 1.36 by an increased phosphate concentration resulted in average total phosphorus removal of 78 + 7%, corresponding with effluent levels of 14 + 4 mg Ptotal/L(9 + 3 mg PO4/3- -P/L). Under these conditions pure spherical struvite pellets of 2–6 mm were produced

Technical and economic feasibility of gradual concentric chambers reactor for sewage treatment in developing countries

A major challenge in developing countries concerning domestic wastewaters is to decrease their treatment costs. In the present study, a new cost-effective reactor called gradual concentric chambers (GCC) was designed and evaluated at lab-scale. The effluent quality of the GCC reactor was compared with that of an upflow anaerobic sludge bed (UASB) reactor. Both reactors showed organic matter removal efficiencies of 90%; however, the elimination of nitrogen was higher in the GCC reactor. The amount of biogas recovered in the GCC and the UASB systems was 50% and 75% of the theoretical amount expected, respectively, and both reactors showed a slightly higher methane production when the feed was supplemented with an additive based on vitamins and minerals. Overall, the economical analysis, the simplicity of design and the performance results revealed that the GCC technology can be of particular interest for sewage treatment in developing countries

Small aggregates can cause nitrite accumulation in one-stage partial nitritation and anammox

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Treatment of low strength sewage with high suspended organic matter content in an anaerobic sequencing batch reactor and modeling application

In this work, an anaerobic sequencing batch reactor (ASBR) was operated for 8 months to treat low strength sewage with high suspended organic matter content. Three phases of operation with increasing organic loading rates (OLR) were performed: 0.4 kg COD/m³ x d (phase I), 0 .8 kg COD/m³ x d (phase II) and 1.2 kg COD/m³ x d (phase III). Adequate stability parameters (pH, total alkalinity) were obtained through all three experimental phases. During phases I and II, the removal efficiencies of organic matter (expressed as total chemical oxygen demand (COD) and total suspended solids ranged between 50-60%. However, these values decreased to 15-25% in phase III. In addition, a non-complex model, including hydrolysis, acidogenesis and methanogenesis, was applied to predict the reactor behavior

Cometabolic enzymatic transformation of organic micropollutants under methanogenic conditions

This is a post-print version of the published article: Gonzalez-Gil, L., Carballa, M., & Lema, J. M. (2017). Cometabolic Enzymatic Transformation of Organic Micropollutants under Methanogenic Conditions. Environmental Science & Technology, 51(5), 2963-2971. https://doi.org/10.1021/acs.est.6b05549Anaerobic digestion (AD) has been shown to have the biological potential to decrease concentrations of several organic micropollutants (OMPs) in sewage sludge. However, the mechanisms and factors behind these biotransformations, which are essential for elucidating the possible transformation products and to foster the complete removal of OMPs via operational strategies, remain unclear. Therefore, this study investigated the transformation mechanisms of 20 OMPs during the methanogenic step of AD with a focus on the role of acetate kinase (AK), which is a key enzyme in methane production. The results from lab-scale methanogenic reactors showed that this step accounts for much of the reported OMP biotransformation in AD. Furthermore, enzymatic assays confirmed that AK transforms galaxolide, naproxen, nonylphenol, octylphenol, ibuprofen, diclofenac, bisphenol A, and triclosan. Except for galaxolide, for which further studies are required to refine conclusions, the OMP’s chemical structure was a determinant for AK action because only compounds that contain a carboxyl or hydroxyl group and have moderate steric hindrance were enzymatically transformed, likely by phosphorylation. For these seven compounds, this enzymatic mechanism accounts for 10–90% of the measured methanogenic biotransformation, suggesting that other active enzymes of the AD process are also involved in OMP biotransformationThis work was funded by Xunta de Galicia through the MicroDAN project (EM 2012/087) and by the Spanish government through the HOLSIA project (CTM2013-46750-R), a Ramón y Cajal contract (RYC-2012-10397) and an FPU Grant (FPU13/01255). The authors belong to CRETUS (AGRUP2015/02) and to the Galician Competitive Research Group (GRC 2013-032)S

Energetic and economic assessment of sludge thermal hydrolysis in novel wastewater treatment plant configurations

Novel wastewater treatment plants (WWTPs) are aimed to be more energetically efficient than conventional ones. Their first step is a chemical oxygen demand (COD) preconcentration stage with different alternatives, such as rotating belt filters (RBF), chemically enhanced primary treatment (CEPT), high-rate activated sludge (HRAS), or combinations thereof, in which energy requirements are substantially reduced. The COD recovered as sludge allows a noticeable increase of biogas production in anaerobic digestion (AD). In conventional WWTPs, sludge anaerobic biodegradability can be significantly enhanced by applying sludge pretreatment methods, such as thermal hydrolysis (TH), before AD. However, considering that novel-sludges are more anaerobically biodegradable than conventional ones, the impact of TH on their methane production is expected to result significantly lower. In this study, an energetic and economic assessment of applying TH in novel WWTPs was performed. We found that TH is only justified to reduce operational costs as long as sludge TS concentration in the feeding to the TH unit is higher than 1-2%. The HRAS is the scenario that leads to the lowest treatment costs (below 1 c€/m3 wastewater if sludge is thickened over 10% of TS). However, the WWTP based on CEPT for COD preconcentration leads to the lowest electricity consumption (below 0.01 kWh/m3 of wastewater), but even in the most favourable conditions the energy autarky was not achievable. Results show that the main impact of TH is mainly due to sludge disposal savings (270,000-430,000 €/year for a 500,000 inhabitants WWTP) rather than the increase of energy production (achieves maximum savings of 35,000-60,000 €/year). Payback time is very dependent on the WWTP size, ranging from 15 to 30 years for a 100,000 inhabitants WWTP and from 2 to 4 years for a 1,000,000 inhabitants WWTPThe authors would like to thank the EU (ID199) and AEI (PCIN-2015-22) for funding, in the frame of the collaborative international Consortium Pioneer_STP financed under Water Joint Programming Initiative. The authors belong to the Gali- cian Competitive Research Group ED431C 2017/029 and the CRETUS Strategic Partnership (ED431E 2018/01). These programmers are co-funded by FEDER (EU)S

Air-side ammonia stripping coupled to anaerobic digestion indirectly impacts anaerobic microbiome

Air‐side stripping without a prior solid–liquid phase separation step is a feasible and promising process to control ammonia concentration in thermophilic digesters. During the process, part of the anaerobic biomass is exposed to high temperature, high pH and aerobic conditions. However, there are no studies assessing the effects of those harsh conditions on the microbial communities of thermophilic digesters. To fill this knowledge gap, the microbiomes of two thermophilic digesters (55°C), fed with a mixture of pig manure and nitrogen‐rich co‐substrates, were investigated under different organic loading rates (OLR: 1.1–5.2 g COD l−1 day−1), ammonia concentrations (0.2–1.5 g free ammonia nitrogen l−1) and stripping frequencies (3–5 times per week). The bacterial communities were dominated by Firmicutes and Bacteroidetes phyla, while the predominant methanogens were Methanosarcina sp archaea. Increasing co‐substrate fraction, OLR and free ammonia nitrogen (FAN) favoured the presence of genera Ruminiclostridium, Clostridium and Tepidimicrobium and of hydrogenotrophic methanogens, mainly Methanoculleus archaea. The data indicated that the use of air‐side stripping did not adversely affect thermophilic microbial communities, but indirectly modulated them by controlling FAN concentrations in the digester. These results demonstrate the viability at microbial community level of air side‐stream stripping process as an adequate technology for the ammonia control during anaerobic co‐digestion of nitrogen‐rich substratesThis research was supported by the European Community Seventh Framework Programme (ManureEcoMine project – 603744); and by the Spanish Government (AEI) through CDTI (SmartGreenGas project – 2014-CE224). The authors belong to the Galician Competitive Research Group ED431C 2017/029 and to the CRETUS Strategic Partnership (ED431E 2018/01), co-funded by FEDER (UE). Computational resources were kindly provided and supported by Fundacion Publica Galega Centro Tecnolóxico de Supercomputación de Galicia (CESGA)S

Why are organic micropollutants not fully biotransformed? A mechanistic modelling approach to anaerobic systems

This is a post-print version of the articleBiotransformation of most organic micropollutants (OMPs) during wastewater treatment is not complete and a drastic decrease of the biotransformation rate with time is reported for many OMPs in different biological processes. To minimize and accurately predict the emission of OMPs into the environment, the mechanisms and limitations behind their biotransformations should be clarified. Aiming to achieve this objective, the present study follows a mechanistic modelling approach, based on the formulation of four models according to different biotransformation hypotheses: Michaelis-Menten kinetics, chemical equilibrium between the parent compound and the transformation product (TP), enzymatic inhibition by the TP, and a limited compound bioavailability due to its sequestration in the solid phase. These models were calibrated and validated with kinetic experiments performed in two different anaerobic systems: continuous reactors enriched with methanogenic biomass and batch assays with anaerobic sludge. Model selection was conducted according to model suitability criteria (goodness of fitting the experimental data, confidence of the estimated parameters, and model parsimony) but also considering mechanistic evidences. The findings suggest that reversibility of the biological reactions and/or sequestration of compounds are likely the causes preventing the complete biotransformation of OMPs, and biotransformation is probably limited by thermodynamics rather than by kinetics. Taking into account its simplicity and broader applicability spectrum, the reversible biotransformation is the proposed model to explain the incomplete biotransformation of OMPsThis research was funded by the Spanish Government (AEI) through the COMETT project (CTQ2016-80847-R) and by an FPU Grant (FPU13/01255). The authors belong to CRETUS Strategic Partnership (AGRUP2015/02) and to Galician Competitive Research Group (GRC ED431C 2017/29). All these programs are co-funded by FEDER (EU)S