Waste strategies for managing excessive sludge in water resources

Abstract

Brazil has been planning to universalize water-related services for a long time. Due to budget constraints, only 40% of overall domestic sewage receive proper treatment before final discharge. Even though, direct sewage discharges represent major threats to Water Resource Managers, it creates challenge to Waste Managers. This study analyzed waste strategies for managing excessive lake sludge. In the selected water resource, raw sewage was discharged directly for a lengthy period. Massive portion of biosolids have accumulated on the bottom of the lake, resulting in considerable sludge layer. A preliminary sludge dredging attempt resulted in algae bloom, steady pollution, eutrophication, and fish death. However, the main expected hazard is the amount of solid waste generated during the sludge removal process. The preferred waste strategy by local officials was disposing the sludge in an open dumping area. Other potential sludge management strategies were: composting; geotextile bags; brick industry (recycling); incinerating; open-dump and landfilling. The results of sludge characteristics indicated no hazardous compounds and a sizable percentage of inorganic matter (85%). Open dump disposal was assumed to be illegal. The landfill solution did not enable any energy or material recovery and should be considered only as the least preferred solution. The geotextile and incineration alternatives indicated to be costly. Composting was considered ineffective due to high inorganic ratio and logistic costs. The low logistics costs and the sludge characteristics makes brick manufacturing comparatively efficient. Therefore, this study proposed as the optimal waste strategy, recycling the sludge as raw material in the local brick manufacturing facility. However, due to severe public budget constraints, the implementation of any sludge management strategy (dredging and disposal) is still contingent on availability of financial resources.