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Abstract
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ABSTRACT
Wastewater sludge treatment and disposal are the most expensive operations carried out by treatment facilities world wide. In most cases. conditioning chemical is the largest single-cost component of the sludge management process. Considering the high conditioner cost. it makes sense to continuously monitor and evaluate the performance of conditioning chemicals used. The selection of a conditioning chemical to aid sludge dewatering, and the detennination of conditioner optimum dosages can be complicated. The type of conditioners to be used would depend on the physical properties of the sludge solids and the specific dewatering process used. The selection of a conditioning chemical depends on the proper evaluation of its effectiveness in enhancing dewaterability. The conditioner selection process, and the calculation of optimum dosages of conditioners to be used, is usually accomplished with jar tests, or in conjunction with dewaterability parameters such as CST, SRF. and TIF. Specific resistance to filtration (SRF) is numerically equal to the pressure required to produce unit rate of flow through a cake having unit weight of dried solids per unit area, when viscosity of liquid is unity [Gale, 1977]. The time-to-filter test involves calculation of the time required for the filtration of sludge or a conditioned sludge sample, rather than the specific resistance. A simple experimental was used to investigate the optimum dosages of lime. alum. ferric chloride, and polymer for dewatering the East Treatment Plant (ETP) sludge because the ETP will treat its sludge in the same way like WTP for better treatment sludge. Our selection for the best conditioner to use for dewatering the ETP sludge was based on the optimum dosages which obtained by SRF and TIF as dewaterability parameters, and the economical study. The experimental work for this study used Lime dosages ranging from 60 to 265 kg/ton SS, alum dosages ranging from 27 to 214 kg/ton SS, ferric chloride dosages ranging from 6 to 30 kg/ton SS, and the polymer dosages ranging from I to 7 kg/ton SS. In the present study, the polymer showed the best conditioner based on the previous characteristics. The polymer is the cheapest conditioner in this study. The values of pH after filtrate have a good ranging from 7.5 to 7. However, it is imported outside the country and it is not the local prepared. That is mentioned as a disadvantage because we ignore its component and its effects on sludge. The ferric chloride cost is 5.5 times the polymer cost. However, it is locally prepared and its effects are well-known. The pH of sludge was increased with the ferric chloride but the values of pH after filtrate are ranging from 7.41 to 6.93. It is recommended to replace the polymer used for conditioning with ferric chloride without adversely affecting the dewatering efficiency. The study also showed that lime cost is 11.2 times the polymer cost. We can have it easily than polymer. The polymer used for conditioning can be replaced by lime without adversely affecting the dewatering efficiency but the pH of sludge increased with lime conditioning more than 9.0. The alum conditioning costs were higher than the other chemicals conditioning.
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