Investigating and modelling the development of septic sewage in filled sewers under static conditions: A lab-scale feasibility study

This paper describes a lab-scale study of the physical and bio-chemical processes associated with the development of septic conditions in sewer pipes filled with static sewage. The study has concentrated on the uptake of oxygen (OUR) and the subsequent changes in chemical oxygen demand (COD), sulphate, sulphide and nitrate concentration and the formation of volatile fatty acids (VFA). OUR of raw sewage ranged from 2 to 13 mg L− 1 h− 1. Apparent nitrate uptake and sulphide generation rates in static sewage varied between 0.2–0.7 mgNO3 L− 1 h− 1 and 0.02–0.05 mgH2S-S L− 1 h− 1, respectively. A logistic function was used to simulate the sulphide generation process in static sewage. It was found that total COD (CODtotal) influenced the apparent sulphide generation rate while nitrate concentrations greater than 4 mg L− 1 controlled the onset of sulphide production in experiments without added sediment phase. Introducing a sediment phase appeared to accelerate hydrolysis and fermentation processes as evidenced by 5–14 times greater dissolved COD generation rates in the bulk water phase.