Seasonal variation pattern of physicochemical and microbial parameters in a wastewater treatment plant

Abstract

According to the statistical analysis results of the samples from the Kabd WWTP obtained over four years from January 2013 to December 2016 and four seasons (winter, spring, summer and fall), the following conclusions are obtained in this study. 1. Variations in the water temperature affect the treatment system, especially the biological treatment system and microorganism population. The sudden temperature rise in summer causes problems for aerobic digestion and nitrification. In addition, the DO of warm water is usually less than that of cold water, and if the temperature suddenly drops during winter, then the bacterial population will be affected. 2. Seasonal variations are observed in the physicochemical parameters. A small variation in pH occurs during all seasons. pH affects the microbial activity in the biological treatment, and an extreme value indicates the presence of toxic material in the wastewater. The electrical conductivity increased as the temperature increased. The maximum average removal of suspended solids, including VSS, depends primarily on the treatment quality process during fall and winter but also depends on the temperature. The removal efficiency is better during fall than that during summer because high temperatures improve the reproduction of nitrifying bacteria and the production of nitrogen in sludge in the final effluent. The SVI in the aeration tanks increased as the temperature increased; however, a value of <150 mg/L indicates filamentous bacteria growth and sudden reproduction. The maximum average removal of BOD5 is equivalent in winter, spring and fall, and these values are higher than that in summer, and the maximum removal of COD is observed in fall. The values of the BOD5 and COD indicate high organic pollution and a large concentration of microorganisms. However, organic substances may present more rapid chemical oxidation than does biological oxidation, and certain organic substances can be toxic to the microorganisms that were used for the 50 BOD5 test. Oxides contributed by dichromate in inorganic substances enhance the organic content and lead to higher COD than BOD values. The maximum average removal of O&G, which is related to the fat and oil content of wastewater, in the secondary treatment level occurs in summer. The fat and oil content related to the food consumed in Kuwait, which usually includes high quantities of butter, meats, nuts, margarine and vegetable fats and oils. 3. Seasonal variations in microbial parameters were observed. The highest average concentrations of coliform count in the raw wastewater were observed in spring, although in the tertiary treatment level, coliform survive better than they do in winter. Salmonella, streptococci and fungi resist and survive better in spring in the inflow wastewater and effluent, and F. coli survives better in the influent and tertiary treatment level in spring. 4. The efficiency of the plant was very good, and it presented a removal efficiency >95% for BOD, COD, TSS, VSS, O&G and % 72 < for NH3-N and PO4-3. 5. The Kabd WWTP followed the KEPA and project contract water standards for irrigation use. All the parameters meet the KEPA and project contract standards, with F. coli and salmonella exceeding the project contract standards.