Mixed agricultural pollutant mitigation using woodchip/pea gravel and woodchip/zeolite permeable reactive interceptors

Dairy soiled water (DSW) is water from concreted areas, hard stand areas and holding areas for livestock that has become contaminated by livestock faeces or urine, chemical fertilisers and parlour washings. Losses of DSW occur as point (e.g. storage, pivot irrigators) and diffuse losses (e.g. during or shortly after land application). The concept of a permeable reactive interceptor (PRI), comprising a denitrifying bioreactor woodchip cell to convert nitrate (NO₃ ^-) to dinitrogen (N₂) gas and an adsorptive media cell for phosphorus (P) and ammonium (NH₄ ⁺) mitigation, attempts to simultaneously treat mixed pollutants. This study is the first attempt to test this concept at laboratory-scale. Washing of woodchip media prior to PRI operation produced low NO₃ ^- but high NH₄ ⁺, dissolved reactive P (DRP) and dissolved organic carbon losses. Dairy soiled water was then treated in replicated PRIs containing woodchip in combination with zeolite or gravel compartments. In general, all PRIs were highly efficient at reducing NO₃ ^-, NH₄ ⁺, DRP, dissolved unreactive phosphorus (DUP) and dissolved organic nitrogen (DON) from an influent water replicating DSW. Longitudinal and hydrochemical PRI profiles, as well as zeolite batch experiments, showed that woodchip can both enhance NO₃ ^- reduction and adsorb nutrients. Since woodchip is likely to become saturated, it is important to place the reactive media cell further into the sequence of treatment. Even though the majority of the dissolved nutrients were mitigated, the PRIs also emitted greenhouse gases, which would need further remediation sequences.