Neutralization of Odours Arising During Dewatering of Municipal Sewage Sludge in the Process of Centrifugal Sedimentation

Emission of unpleasant odours is noxious for both plant workers and residents of surrounding areas, where odours are emitted. In the case of low emissions, the concentration of odour substances are low, and despite of the low odour detection thresholds, they cause significant noxiousness, it is possible to use masking agents. This issue is within range of interest of Division of Water-Sludge Technology and Waste Utilisation of Koszalin University of Technology, where for a few years works are conducted on production of an effective and inexpensive agent for decreasing nuisance of odours. Natural essential oils extracted from fresh plant materials in the process of steam distillation are used as masking agents. The aim of this study was to present a method of reduction of odour nuisance during dewatering of municipal sewage sludge by dosage of the essential oil to sewage sludge. Research on the use of essential oils for masking of odours were divided into two stages. In the first stage of the research essential oil of lemon in the process of steam distillation was produced. Then, produced oil was used in the second stage of research as an agent for masking odour during municipal sewage sludge dewatering. Sludge dewatering process was carried out on a laboratory centrifuge MPW 350. As a input to dewatering process a real stabilized in the process methane fermentation sludge was used, taken from the Wastewater Treatment Plant Jamno, directly from the pump pipe connecting fermentation tanks with centrifuges. Constant parameters of centrifugal sedimentation were: rotation time t [min.] (assumed centrifugation time t = 1 min.) and rotation speed n [rpm] (assumed n = 2400 rpm). Independent variable process parameters were: dose of flocculant C [kg/Mg of dry mass] and dose of essential oil D [cm(3)/100 cm(3) of sludge]. Essential oil, which was produced from lemon was dosed to the feed (sewage sludge with flocculant) before dewatering process in four doses: D-1 = 0 cm(3) of oil/100 cm(3) of sludge, D-2 = 2 drops of oil = 0.06 cm(3)/100 cm(3) of sludge, D-3 = 4 drops of essential oil = 0.12 cm(3)/100 cm(3) of sludge and D-4 = 6 drops of essential oil = 0.18 cm(3)/100 cm(3) of sludge and then period of time of essential oil smell lasts in eluate and sludge after centrifugation process was examined. The study showed that the essential oil of lemon effectively neutralizes odours of sludge and eluate, produced during dewatering of municipal sewage sludge on the laboratory sedimentation centrifuge. With an increasing dose of essential oil of lemon, time of neutralisation of odours after dewatering is increasing, both for the dewatered sludge and eluate. It was also found that essential oils as hydrophobic substances have additional function of coagulants or flocculants, and improve the quality of the mechanical dewatering.