The study investigated the unbiodegradable fraction of particulate chemical oxygen demand (PCOD) in thickened waste activated sludge (TWAS) using semicontinuous-flow completely-mixed anaerobic digesters. A laboratory-scale semicontinuous stirred tank reactor was used to investigate TWAS anaerobic biodegradability at hydraulic retention time of 16.7 d to 33.3 d and organic loading rate (OLR) of 1.21 kg COD/m3•d to 3.47 kg COD/m3•d. The COD and volatile suspended solids (VSS) removal for TWAS were 37% to 44% and 39% to 42% at an OLR of 1.27 and 3.47 kg COD/m3•d, respectively. Using a biomass yield (
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The effect of fine grits and fine debris concentrations on the MLVSS/MLSS ratio of an activated sludge system.
J Environ Sci (China)
January 2025
Low-carbon Water Environment Technology Research Center, School of Environment & Natural Resources, Renmin University of China, Beijing 100872, China. Electronic address:
This study embarks on an explorative investigation into the effects of typical concentrations and varying particle sizes of fine grits (FG, the involatile portion of suspended solids) and fine debris (FD, the volatile yet unbiodegradable fraction of suspended solids) within the influent on the mixed liquor volatile suspended solids (MLVSS)/mixed liquor suspended solids (MLSS) ratio of an activated sludge system. Through meticulous experimentation, it was discerned that the addition of FG or FD, the particle size of FG, and the concentration of FD bore no substantial impact on the pollutant removal efficiency (denoted by the removal rate of COD and ammonia nitrogen) under constant operational conditions. However, a notable decrease in the MLVSS/MLSS ratio was observed with a typical FG concentration of 20 mg/L, with smaller FG particle sizes exacerbating this reduction.
View Article and Find Full Text PDFPrimary sedimentation modelling with characterized setting velocity groups.
Water Res
February 2021
Future Water Institute, New Engineering Building, University of Cape Town, Rondebosch, 7701, Cape Town, South Africa.
Within a plantwide water and resource recovery facility context, an important requirement for a primary sedimentation unit model is the correct fractionation of the settleable portion (primary sludge - PS) of the raw wastewater total suspended solids (TSS) according to the (i) unbiodegradable particulate organic (UPO), (ii) biodegradable particulate organic (BPO), and (iii) inorganic settleable solid (ISS) components. This paper focuses on improving a current TSS- based primary settling tank (PST) model to account for correct proportions of these three components, with characterized settling velocity groups. The steps taken towards development of the primary sedimentation unit model involved the development of a discrete particle settling model in Microsoft Excel and the utilisation of well characterised municipal wastewater data from previous studies in the discrete particle settling model, to reproduce PS and settled wastewater outputs in settling fractions of UPO, BPO and ISS, via steady state and dynamic calculations and under strict material mass balances.
View Article and Find Full Text PDFEstimation of the Unbiodegradable Fraction of Thickened Waste Activated Sludge.
Water Environ Res
September 2018
The study investigated the unbiodegradable fraction of particulate chemical oxygen demand (PCOD) in thickened waste activated sludge (TWAS) using semicontinuous-flow completely-mixed anaerobic digesters. A laboratory-scale semicontinuous stirred tank reactor was used to investigate TWAS anaerobic biodegradability at hydraulic retention time of 16.7 d to 33.
View Article and Find Full Text PDFAn 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.
View Article and Find Full Text PDFDegradation of the unbiodegradable particulate fraction (XU) from different activated sludges during batch digestion tests at ambient temperature.
Water Res
July 2016
Eawag: Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, Dübendorf, 8600, Switzerland; Institute of Environmental Engineering, ETH Zürich, Zürich, 8093, Switzerland.
One strategy for the management of excess sludge in small wastewater treatment plants (WWTPs) consists in minimizing the excess sludge production by operating the WWTP at very long solids retention times (SRTs > 30 days). A number of recent studies have suggested that sludge minimization at very long SRT results from the degradation of the unbiodegradable particulate fraction (XU) (influent unbiodegradable compounds and endogenous decay products). But the biodegradability of the unbiodegradable particulate fraction has only been evaluated during batch digestion test performed at ambient temperature with sludge fed with synthetic wastewaters.
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