2017 ASHS Annual Conference

Agrichemical runoff poses environmental threats if left untreated. In this study, a combination of mixed deciduous species woodchips followed by calcined mineral substrates were used as two-stage bioreactors. The wood chips served as a carbon source for denitrifying bacteria to reduce the nitrate load and the calcined minerals as an adsorptive substrate to reduce phosphorus load from simulated effluent. Microbe mediated processes and adsorptive processes govern the rate and efficacy of these treatments in applications that are intended to provide recycled irrigation water to nursery and greenhouse growers, or to mitigate the harmful impacts that untreated runoff may have on surrounding environments. Woodchip bioreactors were subjected to either a standard nutrient only (20 ppm NO3, 4 ppm PO4 - derived from potassium nitrate and monopotassium phospate) or a nutrient and organophosphate (Chlorpyrifos – Lorsban 4E at a 1 mg a.i. /L rate) enriched influent at a rate of 4 gallons/day for a 3-4 day hydraulic retention time. The remediation potential for phosphorus, which is often the limiting factor in eutrophication, of two highly adsorptive aggregates: a calcined (superheated) clay (Turface MVP) and a calcined shale (haydite) were compared. Properties of these substrates, as well as their potential use in an in-situ water treatment system were investigated during this. The calcined clay had a measured cation exchange capacity (CEC) of 10 meq/100g and the CEC of haydite was 4.8 meq/100g. The phosphorus binding capacity of the calcined clay was reduced by initially present levels of phosphorus (48 ppm), compared to the 2 ppm levels found in haydite. Throughout the 10 week denitrifying microbe incubation process, prior to Chlorpyrifos injection, composite samples of all calcined clay effluent samples contained higher phosphorus levels than the haydite counterpart, despite the same influent P loads. Furthermore, due to particle size, the calcined clay was prone to wash out with the effluent, while the haydite was not. The effects of the bioreactors on nutrient and chlorpyrifos effluent remediation will be presented.