Critical Design and Process Control Features to Optimize Biological Nutrient Removal in Temperate Climates

Biological nutrient removal (BNR) is being selected as the cost effective option for enhancing nutrient removal at plants located in temperate climates in the Chesapeake Bay Watershed and the Long Island Sound in the U.S.A. However, there is considerable discrepancy in the reported values for temperature sensitivity for nitrification and denitrification rates in winter, as observed at different plants and those reported in higher strength wastewaters in Europe and South Africa. Full scale data show that the temperature sensitivity for nitrification is considerably lower. Denitrification rates in the primary anoxic zone are also lower, possibly because of lower influent strengths (250 to 450 mg/L COD). Secondary clarifier limitations have been a key cost factor in attempting year round nitrogen removal as against seasonal (summer) nitrogen removal. The anoxic MCRT and anoxic volume requirements have been a critical cost factor in designs. Split flow designs, where a fraction of the influent flow is sent directly to the anoxic zone, have allowed process designs with lower anaerobic volumes. The readily available COD in the fraction of the influent which enters the primary anoxic zone enhances denitrification rates. Though the anaerobic cell receives less than 100 percent of the influent flow, excellent biological phosphorus removal can still be maintained with phosphate detergent ban wastewaters. The fraction of biomass maintained under anaerobic conditions (and the anaerobic volume) can be reduced because the phosphate detergent ban has decreased the amount of phosphorus which has to be removed for the same influent COD. Biofilm and suspended growth systems have been combined in a single reactor to reduce volume requirements for nitrogen removal.</jats:p

Experience with the design and operation of sustainable wastewater treatment facilities for pollution control and water reuse in Morocco and Jordan

Operating experience at municipal wastewater treatment plants (WWTPs) in Morocco was used to develop design criteria and operating procedures for the construction of two new WWTPs in Shobak and North Shouneh, Jordan to treat septage from small communities to water reuse standards. The WWTPs use an anaerobic/settling digestion tank, facultative lagoons, intermittent or recirculating sand filters, and reed beds to remove solids, carbon, nitrogen, and pathogens. The facilities are sustainable in that they minimize the use of complex mechanical and electrical equipment, do not require chemicals or high electrical demands, and produce beneficial products for the communities which include irrigation water, reeds, and dried biosolids that can be used as a soil amendment.</jats:p