Abstract
Measuring performance has been arguerably, one of the metric with many facets with different school of thoughts, as there exist different approaches of measuring it. Several of the existing approaches measure such metric by comparison with standards esherined in policy documents and as a result, takes less look to its compliance and reliability of values being matched to an established standards. This study seeks to integrate reliability and compliance into measuring of performance of Waste Stabilization Pond (WSP) and Treatment Plant (TP) as well as to generate the appropriate standard chart tables using the Ghana Environmental Protection Agency (EPA) approved discharge values for physico-chemical and some biological parameters to account for these shortfalls on over reliance of EPA discharge standards. Probability distribution density function was applied on the lognormal distribution function to establish the relationship between the statistical coefficient of variation and the coefficient of reliability based on rth moment about the origin in the moment of generation function to generate the functions of the mean and standard deviation, properties of the standard Z normal distribution were used to establish the coefficient of reliability relationship depending on the coefficient of variation influenced by the standard of deviation. Discharge values of Physico-chemical Parameters measured from the WSP were found be performing acceptably based on the EPA standards, whereas only four of the TP were acceptable. Discharge Values of physico-chemical and biological parameters which are found to be accepted under comparison with EPA standards were found to have compliance levels below what is generally accepted for Waste Stabilization Ponds (WSP) designed compliance. Based on these shortcomings, reference charts were develop to serve as reference points in assessing the various characteristics of compliance and performance of WSPs in Ghana on (28) physico-chemical and biological parameters. These charts are intended to make it easier to assess the performance of WSPs and its corresponding reliability and compliance level to compensate for overreliance on EPA standards alone.
Highlights
The use of Waste Stabilization Ponds (WSPs) as an economical and efficient way of re-cycling water has taken centre stage for the use in agricultural production over the past two decades, it’s been noted that, WSPs are usually the most cost effective procedure in dealing with domestic and municipal wastewater treatment for agricultural purposes in Africa due to the condition of favorable climate and low cost of maintenance (Mara, 2004), which are very important factors for tropical countries such as the sub-Saharan Africa.Owing to the natural process of treatment of water in WSP, the treatment processes are highly dependent on the physical design of the WSPs; these physical designs do not consider the ecological process, which takes place in the system
As presented in several studies (Niku et al, 1979; MetCalf and Eddy, 2003; McBride and Ellis, 2001; McBride, 2003; Olieveira and Sperling, 2008; Oakley et al, 2000; Redda, 2013) the Coefficient of Reliability (COR) tells the values of the mean design concentrations to the standard that should be achieved, on a probability basis according to the desired level of the operators of the treatment plant, while the standard normal variate calculates the expected percentage of compliance with the discharge standards
Result of effluent discharge performance are much to be desired when the effluent discharge is compared to the fixed standard value only and where it is assume that if the discharge concentration is less than the standard value, the performance is good and indicates a better compliance level of the WSPs
Summary
The use of Waste Stabilization Ponds (WSPs) as an economical and efficient way of re-cycling water has taken centre stage for the use in agricultural production over the past two decades, it’s been noted that, WSPs are usually the most cost effective procedure in dealing with domestic and municipal wastewater treatment for agricultural purposes in Africa due to the condition of favorable climate and low cost of maintenance (Mara, 2004), which are very important factors for tropical countries such as the sub-Saharan Africa. Several studies (Haydeh et al, 2013; Shah, 2008; Oliveira and Sperling, 2008; Mbwele et al, 2003) have evaluated the performance of the WSPs by comparing the percentage of removal of Biochemical Oxygen Demand (BOD5), Total Nitrogen (TN), Total Suspended Solids (TSS), Total Phosphorus (TP), Total Coliform (TC), Faecal Coliform (FC) and Salmonella with design standards, with few focusing on the extend of compliance of the ponds to its design standards. Few works (Redda, 2013; Oliveira and Sperling, 2008) have compared the percentage of removal of the parameters of evaluation performance of WSPs to the compliance and reliability of the WSPs according to the standards set up by the local policy. This study seeks to integrate reliability and compliance into measuring of performance of WSP and treatment plant as well as to generate the appropriate standard chart tables using the Ghana EPA approved discharge values for physico-chemical and some biological parameters to account for these shortfalls on over reliance of EPA discharge standards
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