Optimisation of sludge management in eThekwini Municipality.

Abstract

Sewage sludge processing for use or disposal has been a continuing challenge for many municipalities within South Africa. The main challenges encountered are the operation complexity and environmental impact posed by sewage sludge handling and disposal methods, along with high capital and operation cost. The problem is getting more complex by the rising volumes of sewage and more stringent disposal regulations. On the other hand, the rising awareness of the beneficial use of this valuable resource is forcing a closer look at how to process sludge effectively to harvest its benefits yet protect public health. This thesis aims to identify optimum alternatives for the sludge management practices within eThekwini municipality as a case study through a semi-quantitative assessment methodology. The principal sludge treatment and disposal methods described in the literature are reviewed and evaluated to determine their comparative performance in; (1) reducing sludge volume/weight, (2) reducing or removal of pollutants, (3) reducing or removal of pathogens, (4) environmental impact, (5) operation simplicity, (6) produced sludge reuse potential, (7) suitability and practicality as an ultimate disposal method, (8) reliability and robustness, (9) sensitivity to sludge quantity and quality change, (10) CAPEX, (11) and OPEX. The findings are compared to the nine years (2010 – 2018) data collected and processed, covering technology used and characteristics (physical, chemical and microbiological) of sewage sludge produced from 25 wastewater treatment works owned and operated by eThekwini municipality. Accordingly, a semiquantitative score has been given to each treatment and disposal method. The semi-quantitative scores are then converted into a single overall score that aided in identifying the optimum sludge management alternatives. Finally, a recommendation for improving the sustainability of the sludge management practices is presented. Moreover, there is not, and will never be, a one-size-fits-all solution. Further investigation needs to be performed from the local economy and geographical context perspective.