Evaluation of a surface flow constructed wetland treating abattoir wastewater

There is a growing need for decentralized wastewater treatment systems that support small abattoirs. Constructed wetlands (CW) are a potential solution; however, research on this subject has been limited to warm climates. Therefore, a research/demonstration site was established at a small-scale abattoir in Great Village, Nova Scotia, Canada. At the site, a 58.5-m² two-celled surface flow CW with Typha latifolia was constructed. On average, the abattoir produced 0.75 m³of wastewater per animal slaughtered (a mixture of cattle, pigs, and lambs) with an annual inflow of 124 m³ and high monthly variability. The residence time of the CW (during the growing season) was determined by a tracer test to be 111 d, and the active volume of the system was 89%. Overall, mass removals during two years of continuous monitoring were BOD₅ (95%), TSS (72%), TDS (81%), TP (88%), SRP (97%), TKN (87%), and TAN (87%). The average E.coli level in wetland effluent (88 CFU 100 mL ^-1) was below the regulatory limit of 200 CFU 100 mL^-1, although 13% of samples exceeded this value. Treatment efficiencies were generally higher during the growing season than the non-growing season.