Climatic criteria for land application of municipal wastewater effluent

Climatic characteristics of the coastal region require design considerations for land application systems that have been largely ignored or the bases for which have been unavailable. For example, the amount of effluent flow in a land application system increases when precipitation occurs, while at the same time the net water requirement of plants decreases. Therefore extra storage and extra land acreage is needed, but the amount required has not been established. Additionally, frequent rainfall coupled with high humidity creates an evaporation regime in the coastal region that inhibits the efficiency and viability of the land application disposal method. The bases of these problems are climatological; therefore, this study uses a climatological analysis to provide design considerations regarding the capability of this disposal method in the coastal region. The availability of long-term digitized daily weather data offers the opportunity to test the design of such systems by simulating multiple years of operation. Simulation using 30 years of weather data for a 3800 m3/d (1 mgd) plant in the southeastern coastal region of the United States shows that the best design requires a 256 ha (640 A) application field and a 16 ha (40 A) storage pond 3.7 m (12 ft) deep. These specifications provide system success ranging from 99% in 6 months of the year to 90% in March and prevent any failures in 90% of the years.