Domestic wastewater treatment by small scale plant and removal of nitrogen and phosphorus

All of the sources of water (river, sea, and lake) are presently suffer high levels of nutrients, due to effluent discharge from wastewater treatment plants, which lead to an increase phenomenon eutrophication and reduce overall water quality efficiency. In addition, there are some cases where treated water is discharged through ground and causing groundwater contamination. As well as most areas outside the city centers are not serviced by the infrastructure thus wastewater is directly fed to the ground without treatment. Then this will causes increase in the nutrients concomitantly damaging the groundwater quality. This status requires more strict regulations for the quality of treated wastewater. Membrane treatment technology is recently considered as one of the most advanced technologies for wastewater treatment in residential areas and has been successfully applied in increasing locations in the world. In addition to the continuous increase in the number of systems operating in this technology, the capacity of these systems is also increasing. In this study, a pilot plant MBR system was studied for the nutrient (nitrogen and phosphorous) removal in domestic wastewater. The bioreactor included equalization, anoxic, oxic and clean water tanks with a submerged membrane. The membrane was a Hollow Fiber (HF) reinforced Polyvinylidene Fluoride Ultrafiltration (PVDF-UF) membrane with pore size of .0.03 μm and total surface area of 12 m2. The activated sludge was recycled to the anoxic/oxic and oxic /equalization chambers of the bioreactor. The results showed higher removal of pollutants for all measured parameters through four runs of operation at different between HRTs and fluxes. The first run was running for a period from 1th until 18th days. The operating conditions were as follows; flux = 25 L.m-2. hr-1 , HRT= 5.4 hr , SRT= 16 days . The results revealed that the maximum of removal efficiency for COD was 71%, for TN was 52% , for TKN was 44%, for TP was 43% , for PO4-P was 77%, while NH4-N removal efficiency was 75%. After 8th day of operation, the pilot plant had a mechanical problems, which affected the removal efficiency and the growth of biomass. As for the second run, the operating conditions were as follows; flux=21 L.m-2. hr-1 , HRT= 6 hr , SRT= 25 days. After day 43rd there was a slight increase in the effluent values and reduction in removal efficiency due to the occurrence of a leakage between the oxic and effluent clean water tanks .The effect of this mixture negatively affected the quality of clean water basin which also adulterated the process of membrane backwashing in the oxic compartment. The third run was a period from 56th until 81th days, where the operating conditions were as follows; flux =16 L.m-2. hr-1 , HRT= 8 hr , SRT =35 days . The results revealed that the maximum of removal efficiency of COD, TN, TKN, NH4-N, TP and PO4-P was 96%, 85%, 95%, 97%, 80% and 87%, respectively. These results showed higher performance of the reactor. The MLSS concentrations during the first, second and third runs were between 500 mg/l and 2500 mg/l. The biomass inittially was supplied from İSKİ Baltalimanı plant with a concentration of 1200 mg/l, but the quality of the active sludge was not high. After 86th day from starting operation, the reactor was supplied with activated sludge from ISKİ Paşaköy İleri Biyolojik Atıksu Arıtma Tesisi, having the concentration of 10000 mg/L and sludge volume index of 92 ml/g. In the following operational period of the reactor, concentration of activated sludge was between 5000 mg/l to 6000 mg/l. Trans Membrane Pressure (TMP) of submerged membrane was between -0.25 – -0.4 bar during the operational periods of the reactors. Fouling of membrane was observed for the days of 45th and 98th of operation by reaching the pressure more than -0.5 bar. Then the fouling layer was removed by chemical washing by Citric Acid. The fourth run was a period from 83th until 117th days. The operating conditions were as follows; flux =16 L.m-2. hr-1 , HRT= 9 hr , SRT= 35 days. The results revealed that the maximum of removal efficiency of COD, TN, TKN, NH4-N, TP and PO4-P was 98%, 79%, 95%, 96%, 86% and 89%, respectively. Two types of ion exchange resins gel (strong cation Model SELION SAC 1000H MB –H+ and anion Model SELION SBA 2000 –Cl-) were used during the second part of the operation.The purpose was to remove additional nitrogen and phosphorous removal, right after the MBR. Also the equilibrium time for each of the ion exchange resins for cation and anion was ( 6.30 hr ) and ( 5 hr ), respectively. In addition, the lowest concentration of ammonium was 0.11 mg/l while the othophosphatase was 0.02 mg/l. The resins were back washed to recover the nutirents and regenerate the resin capacity. The recovered nutrients in the solute were as 109.4 mg/l TN, 70 mg/l NH4-N, 81.9 mg/l TKN, 49.5 mg/l TP and 36.1 mg/l PO4-P. The highest quality of water was obtained at 5 hr adsorption period. The results of TN, TP, NH4-N, TKN and PO4-P. Were 1.1 mg/l , 0.72 mg/l ,0.16 mg/l, 0.81 mg/l and 0.09 , respectively.