Impact of Seasonal Variation on Treatment of Swine Wastewater

Swine wastewater (agricultural wastewater) is normally stored in a storage holding tank for a certain time before released to the other treatment units, such as anaerobic lagoon and aerobic wetland. One of the characteristics for this treatment approach is that all the processes are open systems that are generally more passive in design and operation. As a consequence, seasonal variability including temperature and precipitation can have substantial impact on treatment efficacy and effluent water quality. This paper examines seasonal impacts of temperature on swine wastewater quality and treatment efficacy at a farm in East Leicester, Nova Scotia, Canada. During warm temperatures denitrification was noticeable in the anaerobic conditions, which would reduce the TSS removal rate from 76.6% in moderate temperatures to 42.1% in the warmest period recorded. Rainfall improved final effluent water quality, although this was shown to be through dilution rather than improvement of treatment efficacy. Following precipitation events the contaminant removals were negatively impacted in the aerobic lagoon, as BOD5 removal decreased from 61.6% before rainfall to 41.5% after rainfall, TSS from 71.4% to 59.3%, VSS from 73.4% to 59.3%, TKN from 59.9% to 42.1%, and NH4+ -N from 51.3% to 41.6%. In comparison to the aerobic conditions, the removal rates were increased for anaerobic condition with the rainfall dilution (e.g., TSS from 18.2% to 34.3%), which lead to an overall treatment improvement for the entire system. Thus the case study data presented in this paper provides an assessment of the operational and design issues that are particularly relevant for passive treatment systems that are used in the agriculture industry.