Abstract
Inadequate wastewater treatment is a major problem in South Africa. Existing wastewater treatment facilities often lack sufficient skilled labour, resulting in partially treated effluent. Increasing eutrophication in surface water bodies indicates that this problem needs rectification. The characteristics of the high-rate algal pond (HRAP) technology makes it an attractive option for effluent polishing in South Africa. It has the potential of simultaneous nutrient removal and nutrient recovery from partially treated effluent. A deterministic design model based on the mutualistic relationship between bacteria and algae in an HRAP was developed. The model includes kinetics of algae, ordinary heterotrophic organisms (OHOs), as well as ammoniaoxidising organisms (ANOs) and their interaction with organic compounds, nitrogen and phosphorus. After preliminary verifications, it was found that the deterministic model accurately represented the kinetics involved with the ammonia and nitrate/nitrite concentrations. However, it was also established that the major limitations of the deterministic model are its exclusion of phosphate precipitation and its failure to incorporate the production of particulate and soluble organics due to the respiration, excretion and mortality processes.
Highlights
The discharge of untreated or poorly treated wastewater is a major problem in developing countries (Mara, 2004; Henze et al, 2008)
The assumption was made that only the ordinary heterotrophic organisms (OHOs), Ammonia-oxidising organisms (ANOs), endogenous residue, algae, and particulate biodegradable organics concentrations would contribute to the volatile suspended solids (VSS)
The preliminary verifications showed that the deterministic model can accurately predict the ammonia and nitrate/ nitrite concentrations but is unsatisfactory in predicting the soluble reactive phosphorus (SRP) concentration, since it did not account for phosphorus precipitation
Summary
The discharge of untreated or poorly treated wastewater is a major problem in developing countries (Mara, 2004; Henze et al, 2008). It can cause high levels of pollution in receiving water bodies, which, in turn, can cause serious harm to the environment (Mara, 2004). In South Africa, waste stabilisation ponds, and HRAPs in particular, may serve as simple and cost-effective options for effluent polishing from underperforming wastewater treatment works (WWTWs). The nutrient removal and nutrient recovery capabilities of HRAPs make them promising for effluent polishing These ponds can potentially serve as a buffer between the underperforming plant and the receiving water body, and reduce eutrophication. Such a model may be applied for investigations of the effectiveness of HRAPs in different climates, determination of main design parameters and the creation of strategies for efficient operation
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