Assessment Of Suitability Of Sludge And Wastewater Quality In Waste Stabilisation Pond System In Accra-Ghana For Agriculture Purposes

ABSTRACT

The objective of this study is to analyse the Physico-chemical and bacteriological parameters, evaluate the performance of domestic sewage ponds at the Accra sewage treatment plant at Legon. The aim is to assess the suitability of the final effluent for irrigation and the quality of sludge for agriculture use. A total of 36 wastewater samples and forty-eighty (48) sludge samples were therefore taken for six (6) consecutive months from the sedimentation tank (inlet) and maturation pond (outlet) of the Legon sewage treatment plant at the University of Ghana Legon campus. The samples were preserved on ice and transported to the CSIR Water Research Institute for laboratory analysis. All the methods of analyses carried out were done according to procedures in the Standard Methods for the Examination of Water and Wastewater (APHA, 2012, 22nd Edition). The wastewater quality parameters used to assess the treatment performance of the WSP were total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammonia, phosphate and E. coli. The results of the laboratory analysis showed that the WSP achieved about 82.2, % 86.8, % 82.8%, 85.2%, 58.7% and 99.9% removal of TSS, BOD, COD, ammonia-nitrogen, phosphate-phosphorus and E.coli respectively. Even though removal efficiency of E.coli was high, it recorded a value of 153x103 cfu /100ml which could not meet the Ghana EPA acceptable standard of 10 cfu/100ml.At p≤ 0.05, there was a significant difference in the levels of Total Suspended Solids (TSS), Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), AmmoniaNitrogen, Nitrate-Nitrogen, Phosphate, and E.coli between influent and effluent samples. The sludge as an organic matter can exert significant influence on the physical, chemical and biological properties of soils. The heavy metals levels were generally acceptable when compared with the Limits for metals brought to agriculture land by sewage sludge in South Africa (SFS, 1998:944; Water Research Commission, 1997. Zinc in stream-1 anaerobic pond ranged from 12.3 to 80.0mg/kg with a mean of 64.7mg/kg. Similarly Zinc in stream-2 anaerobic pond ranged from 62.8 to 82.3 mg/kg with a mean of 69.9 mg/kg. The results show that total nitrogen, total phosphorus and total potassium levels in the sludge are also generally satisfactory to produce organic compost (manure). Total nitrogen in stream1 anaerobic pond ranged from 16800 to 19000 mg/kg with a mean of 17800 mg/kg. Total phosphorus ranged from 350 to 410 mg/kg with a mean of 380 mg/kg and total potassium 206 to 210 mg/kg with a mean of 210 mg/kg. There was no significant difference in the levels of heavy metals and the nutrients levels between the stream-1 and stream-2 ponds of the sludge quality at p≥ 0.05. The sludge which accumulates in the Legon sewage treatment plant can be used as a soil improver without posing any environmental hazards. It can be used in agricultural practice in order to maintain and improve soil fertility and crop yield.