Pilot-scale comparison of biological nutrient removal (BNR) using intermittent and continuous ammonia-based low dissolved oxygen aeration control systems

Sensor driven aeration control strategies have recently been developed as a means to efficiently carry out biological nutrient removal (BNR) and reduce aeration costs in wastewater treatment plants. Under load-based aeration control, often implemented as ammonia-based aeration control (ABAC), airflow is regulated to meet desired effluent standards without specifically setting dissolved oxygen (DO) targets. Another approach to reduce aeration requirements is to constantly maintain low DO conditions and allow the microbial community to adapt to the low-DO environment. In this study, we compared the performance of two pilot-scale BNR treatment trains that simultaneously used ABAC and low-DO operation to evaluate the combination of these two strategies. One pilot plant was operated with continuous ABAC while the other one used intermittent ABAC. Both processes achieved greater than 90% total Kjehldal nitrogen (TKN) removal, 60% total nitrogen removal, and nearly 90% total phosphorus removal. Increasing the solids retention time (SRT) during the period of cold (∼12 °C) water temperatures helped maintain ammonia removal performance under low-DO conditions. However, both processes experienced poor solids settling characteristics during winter. While settling was recovered under warmer temperatures, improving settling qual ity remains a challenge under low-DO operation.

Oxygen requirements in relation to sludge age in wastewater treatment plants

Sustainability of activated sludge (AS) wastewater treatment processes is inexplicably linked to minimization of secondary wastes, such as waste sludge, as well as energy requirements for achieving effluent quality standards. Oxygen requirements and waste sludge management accounts for most of energy consumption in aerobic AS wastewater treatment plants (WWTPs). In this study, a novel, highly aerobic AS process, entitled complete solids retention AS process (CRAS), is being evaluated in terms of waste sludge production and biomass oxygen utilization rate. Aim of this work is to study the effect of solids retention time (SRT) on observed sludge yields and on oxygen requirements for respiration in order to evaluate CRAS process as a sustainable alternative to typical activated sludge processes.

Application of polyelectrolytes for improving the dewatering performance of drinking water treatment sludge using geotextiles

The sludge generated at drinking water treatment plants (WTPs) is a high-moisture content residue, and therefore difficult to handle, transport, dispose of or recover. During the last decades, geotextile tubes have been successfully applied to reduce the residue volume, facilitate its handling and subsequent reuse. This study aimed to understand the factors that interfere in the filtration and dewatering efficiencies and to experimentally analyze the dewatering process of WTPs sludge, evaluating different test procedures and investigating the influence of the type and dosage of polymeric additives on dewatering performance. Geotextile cone dewatering tests and geotextile bag dewatering tests were performed, using four different woven geotextile samples and an aluminum sulfate WTP sludge sample. The results showed that the use of geotextile cone dewatering tests for geotextile selection and for additive selection and dosage was representative for the dewatering process intended, reflecting the results verified in the geotextile bag dewatering tests. Sludge chemical conditioning increased dewatering rate and solids retention during the tests’ early stages, but it did not result in a higher final solids content sludge cake. Keywords: dewatering systems, geosynthetics, waste management.

Operation of Submerged Anaerobic Membrane Bioreactors at 20 °C: Effect of Solids Retention Time on Flux, Mixed Liquor Characteristics and Performance

Four flat-sheet submerged anaerobic membrane bioreactors ran for 242 days on a simulated domestic wastewater with low Chemical Oxygen Demand (COD) and high suspended solids. Organic loading was maintained around 1.0 g COD L−1 day−1, while solids retention time (SRT) was varied from 20–90 days. This was achieved at a constant membrane flux, maintained by adjusting transmembrane pressure (TMP) in the range 1.8-9.8 kPa. Membrane fouling was assessed based on the required TMP, with mixed liquors characterised using capillary suction time, frozen image centrifugation and quantification of extracellular polymeric substances (EPS). SRT had a significant effect on these parameters: fouling was least at an SRT of 30 days and highest at 60 days, with some reduction as this extended to 90 days. Operation at SRT <30 days showed no further benefits. Although operation at a short SRT was optimal for membrane performance it led to lower specific methane productivity, higher biomass yields and higher effluent COD. Short SRT may also have accelerated the loss of essential trace elements, leading to reduced performance under these conditions. A COD-based mass balance was conducted, including both biomass and methane dissolved in the effluent.

Temperature Phased Anaerobic Digestion at the Intermediate Zone of 45 °C: Performances, Stability and Pathogen Deactivation

Temperature phased anaerobic digestion (TPAD) systems with conventional sequences (first stage of 55 ℃ and second stage of 35 ℃) have been widely studied. However, very limited studies were available on TPAD system with the first stage operated at the intermediate zone of 45 °C, mainly due to the notion that limited microbial activity occurs within this zone. The objective of this research was to evaluate the performance, stability and the capability of 45 °C TPAD in producing class A biosolids, in comparison to a conventional TPAD. Four combinations of TPAD systems were studied, 45 ℃ TPAD 2.5/10 (1st stage solids retention time (SRT) 2.5 days/2nd stage SRT 10 days), 45 ℃ TPAD 7.5/10, 55 ℃ TPAD 2.5/10 and 55 ℃ TPAD 7.5/10. Among all, 45 ℃ TPAD 7.5/10 was found to have the best performances, attributed to its high volatile solids (VS) destruction (58%), minimal acetate accumulation (127 mg/L), high methane yield (0.58 m3 CH4/kg VS removed), high COD destruction solid COD (sCOD; 74% and total COD (tCOD) 54%) and minimal free NH3 content (67.5 mg/L). As for stability, stable pH distribution, high alkalinity content and low VFA to alkalinity ratio, indicated a well-buffered system. Additionally, the system had also able to produce class A biosolids. Therefore, proved that TPAD system operated at the intermediate zone of 45 ℃ can perform better than the conventional TPAD, hence, highlighting its economic advantage.

Use of Various Thin-Layer Settling Schemes for Industrial Wastewater Treatment

In this paper, the theoretical preconditions in favor of the use of thin-layer settling tanks for industrial wastewater treatment are substantiated by the corresponding laboratory studies. The data from the results of studies of wastewater treatment of the textile, knitwear and silk industries conducted on laboratory thin-layer settling tanks according to the basic schemes of wastewater supply and precipitating sediment are given. As stated by these data, according to the generally accepted criteria for the effectiveness of suspended solids retention for wastewater of the above-mentioned industries, it is more preferable to use thin-layer sedimentation in a cross-sectional scheme.