A two stage membrane treatment of secondary effluent for unrestricted reuse and sustainable agricultural production

Field experiments are in progress for secondary wastewater upgrading for unrestricted use for irrigation and sustainable agricultural production. The integrative treatment system for the secondary effluent polishing is based on implementing in series of two main treatment stages: ultrafiltration (UF) and reverse osmosis (RO) membrane treatment. The pilot system has the capacity of around 8 m3/h. The UF effluent is used to feed the RO membrane stage. Different mixtures of UF and RO permeates are subsequently applied for drip irrigation of various agriculture crops. The field results indicate the importance of the UF component in the removal of the organic matter and the pathogens that are still contained in the secondary effluent (the secondary effluent is obtained from a waste stabilization pond treatment system). Under specific conditions, when the dissolved solids content is relatively low, the UF effluent can be applied directly for unrestricted irrigation. In the successive RO stage most nutrients are removed, allowing applying the effluent without jeopardizing the soil fertility and the aquifers. Preliminary economic assessment indicates that the extra cost for effluent polishing via the UF stage only is in the range of 8–12 US cents/m3. The extra cost for the RO stage is as well assessed at 8–12 US cents/m3. The additional treatment expenses depend to a large extent on the quality of the incoming raw secondary effluent and local requirements at the command agricultural production sites.