Innovative production treatment hydroponic farm for primary municipal sewage utilisation

Abstract

The objectives of this work were to investigate a conceptual layout for an inexpensive and simple system that would treat primary municipal wastewater to discharge standards. Furthermore, the system may provide an increased supply of safe water for irrigation with low operational costs and produce commercially valuable plants for small communities in arid and semi-arid areas. A commercial hydroponic system was adapted for this study and consisted of five gullies, 3 m long by 100 mm wide. Primary treated effluent was used to irrigate lettuce in one series and a commercial nutrient solution was used to irrigate the same type of lettuce in another series as a control, both by nutrient film technique (NFT). Nutrient and suspended solids were efficiently removed by the NFT plant system. While no uptake of F-RNA bacteriophages were detected within lettuce leaves, uptake was apparent from spiked virus-sized particles (fluorescent 0.1 μm microspheres) and equivocal from spores of the faecal bacterium, Clostridium perfringens. Microbial data was used in a β-Poisson dose response model and indicated that the probability of infection for a single ingestion event of NFT grown lettuce grown on primary treated municipal effluent was about 1.7% for viruses. Moreover, plants accumulated heavy metals in leaf tissues at concentrations higher than the maximum recommended levels for Australian and New Zealand food (As=6.5, Cd=3.8, Pb=20 mg kg −1). Hence, it is recommended to evaluate ornamental or non-edible crops, such as essential oils, pyrethrum or flowers for sewage treatment. A conceptual layout for a full-scale production treatment hydroponic farm (PTHF) for small communities was based on modelling phosphorus removal with the hydroponic NFT experimental pilot plant. With NFT culture of lettuces, roots and other surfaces accounted for 67–72% of total phosphorous (TP) removal (by adsorption mechanisms). Based on empirical modelling, an influent TP 2–6 mg l −1 PTHF would be expected to be economical for small communities (<400 people) and produce effluent with TP <0.15 mg l −1, SS <2.5 mg l −1 and BOD <55 mg l −1. Lower values would be expected if the effluent was polished through a humus filter.