Removal of nitrogen and phosphorus from swine wastewater by the activated sludge units with the intermittent aeration process

Abstract

Nitrogen and phosphorus removal in fill-and-draw type activated sludge units with an intermittent aeration process (IAP) was evaluated with typical wastewater from swine housing (total N/BOD 5 ratios were 0.18, 0.31 and 0.45), in comparison with a non-limited aeration process (a conventional process, NLAP), under 0.50 kg m −3 d −1 BOD loading for each unit in bench scale. Operational conditions for the units were the same except for the aeration program; in the NLAP, a conventional consecutive aeration for 21 h was adopted, whereas in the IAP, aeration was intermittent and aeration and non-aeration periods were alternated at intervals of 1.0 h (IAP-1.0) or 3.5 h (IAP-3.5). When the units were high in MLSS concentrations, high removal efficiencies (89.0–99.5%) for BOD and TOC were attained with both IAP and NLAP in all runs. While, large differences in the removal of nitrogen and phosphorus between IAP and NLAP were observed; at influent N/BOD 5 of 0.18, removal efficiencies for total nitrogen in IAP-1.0 and NLAP were 96.9 and 58.6%, and for total phosphorus were 80.8 and 47.8%, respectively. However, those removal efficiencies decreased with the increase in the N/BOD 5 ratio of wastewater charged. Removal efficiencies for total nitrogen in IAP-1.0 was 72.2%, even at influent N/BOD 5 of 0.45. Thus, high removal efficiencies for organic substances, nitrogen and phosphorus in swine wastewater were simultaneously obtained by IAPs. By adopting an adequate aeration program for individual swine wastewater treatment, this system will provide a promising means for nitrogen and phosphorus control without pH control, divided change of wastewater or addition of methanol.