Modeling sulfide production in full flow concrete sewers based on the HRT variation of sewerage.

The corrosion and odor in concrete sewers are mainly related to the sulfide production, which is, under certain circumstances, directly proportional to the hydraulic retention time (HRT) of the sewer. To reduce the corrosion and control the odor in concrete sewers, it is necessary to model the production of sulfide in the concrete sewers with different HRTs. However, previous researches were mostly carried out in simulated Perspex-made sewers, and the obtained theoretical formulas based on the Monod equation were impractical because of the complexity. An actual concrete pipe with domestic sewage was employed in this study to obtain a simple but practical model, which can be applied to quantitively describe the sulfide production according to the HRT of the sewer and the chemical oxygen demand (COD) of the sewage. The empirical equation obtained was rs = (0.045 × lnHRT + 0.071) × ([COD] - b)0.6, the coefficient is a logarithmic function of the HRT, and the sulfide production rate and COD have a power relationship. Based on the data of COD and HRT obtained in the realistic sewer, the production of sulfide in the sewer can be predicted for better maintaining sewers through sulfide control.

Sludge characteristics, system performance and microbial kinetics of ultra-short-SRT activated sludge processes.

Activated sludge processes with an ultra-short sludge retention time (ultra-short-SRT) are considered to have potential for energy and resource recovery from wastewater. The present study focused on the sludge characteristics, system performance and microbial kinetics in ultra-short-SRT activated sludge (USSAS) processes using typical domestic wastewater (SRT = 0.5, 1, 2, 3 and 4 d). The results showed that compared with the sludge in conventional activated sludge (CAS) processes, the sludge structure in USSAS system was looser (fractal dimension, D2P, 1.19-1.33), the boundary was rougher (pore boundary fractal dimension, DB, 1.44-1.59), the sludge concentration was lower, and the sludge volume index (SVI) was higher; bacteria such as Thiothrix and Trichococcus that cause sludge bulking, which poses an operation risk, were extensively detected, especially at SRTs of 0.5 d and 1.0 d. The performance in terms of total chemical oxygen demand (tCOD) and phosphorus removal increased with increasing SRT, and the highest removal rate (approximately 85% for tCOD and 90% for phosphorus) was observed when the SRT was 4 d. Both bioconversion and biosorption were responsible for the C/P separation, and their roles were different for different types of organic matter and phosphorus under different SRT conditions. The proportion of phosphate-accumulating organisms (PAO) reached 2.4% when the SRT was 3 d, resulting in highly effective biological phosphorus removal. The values of microbial kinetic parameters such as YH and KdH in USSAS systems were higher than those in CAS systems, indicating faster microbial community renewal. This study was helpful for understanding the characteristics of USSAS process.