Modification of the Multi-Stage Treatment (Anaerobic- Anoxic- Oxic) by Adding Almond Shells as Biological Carriers

In this study, the treatment process Anaerobic- Anoxic- Oxic (A2O) was modified by adding almond shells as biological carriers. The performance of it has been evaluated in two groups for simultaneous removal of organic matter and nutrients (nitrogen and phosphorous) from wastewater. In both groups the hydraulic retention time (HRT) was 12.5 hours and mixed liquor suspended solid (MLSS) was 2000 mg/L. In the first group: The Oxic bioreactor was filled with packing up to 7% on an effective volume basis. In the second group: All bioreactors were filled with packing up to 7% on a volume basis for each tank. The efficiency of the two groups was compared by analyzing the removal efficiencies of COD, SS, NH4+-N, PO4-3. The removal efficiency in the first group was 94.71%, 90.52%, 95.73% and 92.55%, respectively, while in the second group was 96.53%, 89.82%, 98.29% and 95.61%, respectively. The treatment when adding shells in all bioreactors is the best, but the SS removal efficiency decreased slightly, the reason for this is due to the degradation of shells (organic matter). Obtained results indicated the good stability of the modified system without adding any external carbon sources whereas the almond shells have the ability to release carbon. Almond shells have the ability to adsorb pollutants and they were excellent carriers for bacteria (Biofilm).