Treatment of Concentrated Nutrients in reject Wastewater of Reverse Osmosis Process treating Tertiary Effluent from Convention

Wastewater reclamation and its reuse for beneficial purposes is a common goal in all countries particularly in water stressed countries around the world. Cutting edge technologies such as reverse osmosis (RO), micro and ultra filtration etc. are often used to purify wastewater effluent generated in conventional systems. However, the rejected wastewater from these processes is usually laden with concentrated nutrients, salts, inorganic materials while it is devoir of organic materials those are removed in the course of treatment. Safe disposal/reuse of these wastewaters is a growing concern. A study was carried out to investigate a number of selected processes that have potential of removing the nutrient concentrates from the reject wastewater. At bench-scale, three most promising processes were developed unifying available unit processes proven to reduce nitrogen and phosphorus in brackish water and they were tested with synthetic RO reject water. The processes were: A. Up-flow sludge blanket filtration process; B. Cascaded aerator system with partial anaerobic condition and C. Denitrifing process with bacterial growth on fixed anaerobic porous media followed by algae pond. Three carbon sources methanol, acetate and glucose were supplied in proportion of chemical composition of biological cell at microbial level. Various concentrations of this carbon sources were tried separately in 79 test cases. Process C appeared to be the best in removing total nitrogen and phosphate at ranges of 81-85% and 87-92% respectively. The process C was tested at pilot scale using actual RO reject wastewater at 1 m/d transported from an advanced wastewater treatment plant in Kuwait. Three months continuous operation generated 55 sets of daily data. The results indicated that in average total nitrogen and total phosphorus concentrations of 76 mg/l and 29 mg/l in RO reject wastewater can be removed by average of 76% and 86% respectively. Average concentration of total nitrogen and total phosphorus in the final effluent remained at 13.9 mg/l and 3.3 mg/l respectively. The unit cost of implementing the process C is expected to be 0.03 KD/m (1KD ≈3.5 USD) without the use of external carbon source. In such case, instead of external carbon source, primary treated wastewater can be mixed with RO reject water and this modification can approximately add about 10 mg/l of BOD5 equivalent in reject water to be treated in the tested process.