Research work has been carried out for more than 20 years by Eparco and the University of Montpellier (France) on the application of biological wastewater treatment processes for small communities. This research has led to a new process which is particularly suitable for remote populations, taking into account several specificities such as as the seasonal fluctuations in the population, the accessibility of the site, the absence of a power supply on site, the reduced area of land available and the low maintenance. Thus, the process, which combines a septic tank operating under anaerobic conditions and a biological aerobic filter, is a solution for wastewater treatment in mountain areas. This paper presents the process and three full-scale applications in the region of the Alps.
A three year field and investigative study carried out on 33 individual sanitation systems showed that the frequency of septic tank emptying could be at least 5 years, corresponding to a sludge accumulation rate of 0.21/user.day. This value should be included in the calculation of septic tank sizing. Other data showed within a septic tank the methanogenesis is only effective after 2 years of operation. Thereby a septic tank should not be desludged before this period of time. At last, among all the physico-chemical parameters monitored to study the sludge quality, the best indicators of system failures were both the solids (TS and VS) and soluble matter (COD and some VFA). Then, biochemical study of septic tank sludge showed that the main hydrolytic enzymes (cellulase, phosphatase, protease, lipase and urease) are present in septic tank sludges and linked to the insoluble particles. Their solubilization with different solvents (buffers, surfactants…) showed each enzyme was linked in a different way.
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