Diagnosis Of Soba Waste Stabilization Ponds' Plant, Deterministic /Mechanistic Model

Abstract

Khartoum's State has two public wastewater treatment plants, of which only one is purely waste stabilization ponds system, i.e. Soba treatment plant. As most researches have proved, the removal rates of the plant is no satisfactory, especially coliforms'. However, most of these studies are concerned with the redesign of the plant or replacing it with a new one, while only a few discuss the factors affecting the treatment process or how to remedy its imperfections. As proper analysis and environmental control can improve almost all wastewater biological treatments; this study basically aims to decide the cause /effect relationship of the removal rates of organic and suspended solid loads with some of the most important environmental conditions, in addition to major constituents' concentrations in the wastewater. This relation can be used to enhance the removal rates of the ponds' system. As the removal efficiency for suspended solids had dropped to as low as 60%, while BOD removal stays above 75% most of the time, compared to the 80% TSS and 85% BOD design removal; the treatment is in desperate need for modification. Based on the effluent/ influent concentrations for a period of 73 months' averages, the relation is expressed as statistically derived equations (deterministic model) using multiple regression analysis, while the strength of it is measured using correlation coefficients and ANOVA tables technique. After eliminating outlier points, the model was drawn with ±95% confidence interval to check its reliability. For further confirmation of the soundness of the stochastic model, it was converted into a mechanistic /phenomenological model using Thirumurthi graphical solution of the well known Wehner & Wilhem equation. The resulting model was compared with the old model and the results were satisfactory in accordance to approach and precision. After the compatibility of the two models is proved, it can be used to improve the performance of the plant by controlling the predominating factors on the treatment to improve the effluent's quality, in addition to improving design of similar plants making use of current experience. As sun shine, dissolved oxygen, pH level, and temperature are the factors with the higher correlation, and consequently having more influence on the quality than the rest of smaller correlation; they can be controlled to v achieve the maximum possible efficiency of the plant using simple inexpensive methods i.e. scum removal, equalization tanks, algal harvesting, etc. As the simplicity and inexpensiveness of stabilization ponds technique is well known, the remediation and quality enhancement has been proven to be no exception. However, researches and experimental work is of major importance in order to find the extent of improvement achieved from the recommended alterations.