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The increasing utilization of waste water sludge and source-separated organic household waste in agriculture has brought the quality aspects into focus, among others the hygienic aspects. In this study, the reducting effect on Fecal Streptococcus (FS) and Salmonella of different methods for stabilization and methods for further treatment of sludge and organic waste has been investigated. The most common methods for stabilization, i.e. aerobic and anaerobic stabilization, only reduce the indicator organisms by approximately 1 logarithmic decade. Methods for further treatment of sludge and organic waste have shown reductions of microorganisms allowing for unrestricted utilization in agriculture, meeting the product control: FS below 100/g and no Salmonella detected. The effect of storage of sludge at summer and winter temperature respectively has been investigated. At temperatures (around 20°C) significant reductions of Salmonella were found, while the die out at low temperatures (below 10°C) was limited. FS was not reduced systematically during storage, and therefore, FS is not usable as indicator organism for the hygienic properties of sludge during storage.

More than three years of pilot-plant operation has documented that inhibition of nitrification was found to influence the dimensioning of the largest Danish wastewater treatment plant, which serves a major part of Copenhagen. Hence, a program for investigating the sources of substances inhibitory to nitrification was initiated. Since the number of substances potentially inhibitory to nitrification is very high, the investigations used direct testing of inhibitory effects on nitrification as a tool for the mapping operations. The overall purpose of the investigation was to determine the types of sources of inhibitory substances and to suggest a program for source control to be implemented by the individual municipalities in the catchment area. This paper describes the strategy for sampling and the results of the first two years of activity. Major conclusions have been that the most important sources of inhibitory substances are to be found among the industries, and that nearly all of the industries investigated exhibited some kind of inhibitory effect Further, is was demonstrated that the toxic unit calculation might be used in the quantification of the sources, and that the observed effects could be explained by the chemical substances in the wastewater from the industries. Based on the above described results, a strategy for control of the inhibitory effects at the different levels of the catchment area was suggested.

A pilot-scale study of membrane bioreactor treatment for reclamation of wastewater from Berendsen Textile Service industrial laundry in Søborg, Denmark was carried out over a 4 month period. A satisfactory COD degradation was performed resulting in a low COD in the permeate (< 50 mg/l). To obtain satisfactory treatment, addition of nitrogen was necessary. The biodegradability of the permeate was very low (BOD5 < 2 mg/l). A hydraulic retention time of 1 d turned out to be sufficient at a sludge concentration of 10 g MLSS/l. Through addition of a cationic polymer, a satisfactory dewaterability of the sludge was reached. Membrane tests showed that operating at a trans-membrane pressure of 3 bar and a cross-flow velocity of 4 m/s, a flux of 120 l/m2h can be expected without using chemicals for membrane cleaning. The quality of the permeate was very good when comparing to the reuse quality demands of water to the wash processes. Reuse of the permeate in all rinsing steps requires additional treatment through reverse osmosis.

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