Dissolved oxygen and idle time effects on sewage bioremediation

Abstract

This paper explores the effects of dissolved oxygen (DO) concentrations and idle time on the performance of aerated-sludge portable sewage systems for rapid deployment during natural calamities or warfare. Using synthetic sewage, three different reactors were operated at DO levels of 2-6 mg/l to determine the optimum DO for reactor performance, chemical oxygen demand (COD) and total organic content (TOC) removal, pH, conductivity and biomass concentrations. Low DO values result in very low COD removal efficiency, while DO levels over 6 mg/l are not significantly more efficient. The oxygen utilisation rate and specific oxygen utilisation rate were in the ranges 0 . 87-1 . 08 mg O 2 /h and 0 . 44-0 . 895 mg O 2 /g MLSS (mixed liquor suspended solids) per hour respectively for the three reactors. The highest achieved specific removal rate was 14 mg/g MLSS per hour and 6 mg/g MLSS per hour for COD and TOC respectively. Investigation of idle time (no-aeration) revealed that an idle time of less than 24 h results in low removal efficiency (COD and/or TOC) but the system recovers in the next 24 h; however, an idle period of 48 h or greater results in very poor efficiency and may cause permanent failure of the bioremediation process. The results of the present study can be applied to avoid system failure in a sewage treatment system as a result of, say, intermittent or sudden power shutdown.

Editorial

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It is my pleasure to welcome you to the June issue of Water Management, which brings together a selection of papers, briefings and discussions on a diverse range of interesting topics. The subsequent four papers focus on complex flow dynamics generated in stilling basins by submerged jets (Zhang et al, 2014) and at reservoir intakes by free surface vortices (Sarkardeh et al, 2014); sanitation issues associated with portable sewage systems (Khan et al, 2014b); and water quality modelling in clean water distribution networks (Seyoum and Tanyimboh, 2014).The accurate determination of water surface profiles for gradually varied flow (GVF) is a classic hydraulic problem of significant importance to water engineers interested in determining the upstream and downstream influence of in-stream structures or works. The subsequent four papers focus on complex flow dynamics generated in stilling basins by submerged jets (Zhang et al, 2014) and at reservoir intakes by free surface vortices (Sarkardeh et al, 2014); sanitation issues associated with portable sewage systems (Khan et al, 2014b); and water quality modelling in clean water distribution networks (Seyoum and Tanyimboh, 2014).

The accurate determination of water surface profiles for gradually varied flow (GVF) is a classic hydraulic problem of significant importance to water engineers interested in determining the upstream and downstream influence of in-stream structures or works.

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“…The two briefing papers in this issue cover gradually varied flow in circular channels (Vatankhah and Easa, 2014) and the weather generator rainfall analysis processing tool Wrapt (Tomlinson et al, 2014). In the paper by Khan et al (2014b), the performance of aeratedsludge portable sewage systems suitable for rapid deployment during such emergencies is explored with respect to the effects of dissolved oxygen (DO) concentrations and idle time due to power cut-off. In their briefing paper, Vatankhah and Easa (2014) present an exact analytical solution to the simplified GVF equation for circular open channels.…”

“…In the paper by Khan et al (2014b), the performance of aeratedsludge portable sewage systems suitable for rapid deployment during such emergencies is explored with respect to the effects of dissolved oxygen (DO) concentrations and idle time due to power cut-off. Natural disasters and armed conflicts can have catastrophic effects on clean water and sewage waste disposal infrastructure, especially in developing countries already short of these facilities.…”