A low volatile fatty acid wastewater from a Barcelona residential area was prefermented in a laboratory-scale primary clarifier operated as a prefermenter-an activated primary tank. Total suspended solids (TSS), oxidation-reduction potential (ORP) and temperature were measured in the prefermenter. Influent and effluent were characterised through chemical oxygen demand (COD), soluble COD, volatile fatty acids (VFA), VFA potential, soluble PO 4-P, NH 4-N, pH and alkalinity. Solids retention times (SRT) of 5 d and 10 d were tested. Best results were obtained for the 5 d SRT with the prefermenter covered for better temperature and ORP control. For these conditions, COD solubilisation was measured as 22 mg COD/l, 66 mg COD/g influent particulate COD, or 91 mg COD/g influent VSS. VFA-formation was measured as 34 mg VFA-COD/l, 142 mg VFA-COD/g influent VSS, or 77 mg VFA-COD/g influent COD. These values indicate remarkable solubilisation and fermentation in the prefermenter. The VFA/PO 4-P ratio was improved from 0.9 to 5.5 mg VFA-COD/mg PO 4-P, but did not approach the recommended value for biological P removal (20 mg/mg). VFA production could not reach the influent VFA-potential either (110 mg VFA-COD/l) and VFA-potential was lower in effluent than in influent. With a 5 d SRT and the prefermenter uncovered, a small VFA formation and no solubilisation were observed. This was interpreted as the VFA being formed from the influent soluble COD. With a 10 d SRT, a very low ORP was measured. Neither solubilisation nor VFA production were detected in the prefermenter. Concurrent acidogenic fermentation and methanogenesis are compatible with these results. P and N solubilisation was low or moderate in the prefermenter over all periods, and increased with increasing SRT and TSS, and decreasing ORP, and pH and alkalinity were quite stable, due to the high influent alkalinity and the moderate VFA formation and N solubilisation.
The VFA-potential method is a fermentation technique for estimating the total volatile fatty acids (VFA) availability in wastewater. The VFA-potential was conceived as a measurement of the readily fermentable COD, because fermentation utilizes this COD as a substrate. However, anaerobic hydrolysis can also be a potential source of fermentable matter. In this work, the VFA-potential method has been modified and simplified to avoid nitrogen gas usage. In the modified method, several conventional BOD flasks are completely filled with wastewater and subsequently opened at scheduled times. This procedure keeps oxidation-reduction potential (ORP) at very low levels while reducing the laboratory equipment required. COD fractionation of initial wastewater was carried out. Analysis of total suspended solids (TSS), soluble phosphate, ammonia nitrogen, total and soluble COD, and individual VFA were obtained throughout the VFApotential test, to evaluate hydrolysis and fermentation. The mean ratio between VFA-potential and the initial total COD was 0.23 mg VFA-COD/mg COD. The VFA to phosphate ratio was in the range of 14.6-22 mg VFA-COD/mg P, which is in accordance with the recommended value for biological phosphorus removal (20 mg/mg). A strong hydrolysis of solids was detected throughout the degradation of TSS and soluble COD. The observed behavior of TSS, soluble COD, and VFA is compatible with a partial utilization of hydrolyzed COD for fermentation. Phosphorus and nitrogen solubilization are described, as well as pH and alkalinity behavior, throughout the test.
A mechanistic model has been developed to model ammonia removal in aerated facultative lagoons. Flow is modeled through the water column by a continuously stirred tank reactor and exchanges between the sludge layer and the water column are simulated by a solids separator. The biological model is based on an activated sludge model with reactions added for anaerobic bacterial growth and degradation of inert organic material. Results show that the model is able to predict seasonal variation in ammonia removal as well as sludge accumulation in the lagoons.
We describe a case of a patient who experienced recurrent COVID-19 pneumonia over a period of 123 days. Neither remdesivir nor convalescent plasma were temporally associated with viral clearance or increased plasma neutralization capacity. Antibody levels remained low until day 151 and cellular immunity increased overtime with no viral evolution.
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