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Effectiveness study of vertical and horizontal aerated steel slag filter for nitrogen removal from domestic wastewater

Nitrogen removal from wastewater often requires a highly cost of chemical treatment to prevent over loading of nutrient in effluent discharge to the surface water body. Rock filters (RF) emerged as one of attractive natural wastewater treatment method to treat wastewater high in nutrient. However, the application of RF in the removal of eutrophic nutrients and nitrogen is very limited under warm climate. Therefore, the aim of this study is to develop an aerated steel slag filter (ASSF) system design under Malaysia condition. The objective of this study are to optimize hydraulic loading rate (HLR) and aeration rate for the vertical flow aerated steel slag filter (VFASSF) system for ammonia nitrogen (AN) and total kjeldahl nitrogen (TKN) removal, identification of nitrifiers in VSASSF system, and comparison study of vertical and horizontal ASSF system on pollutant removal. Three pilot-scale VFASSF with 2.0 m H and 0.3 m D and a HFASSF with 1.0 m L and 0.3 m W and 0.5 m H has been developed at Taman Bukit Perdana Wastewater Treatment Plant (WWTP) Batu Pahat, Johor to optimize the HLRs range from 0.16 - 5.44 m3/m3.d and aeration rate of 3, 5 and 10 L/min for nitrogen removal from domestic wastewater. During the optimization study, the VFASSF influent and effluent daily composite sampling analysed for TKN, AN, DO, and temperature. Whilst, for monitoring the effectiveness of the VFASSF and HFASSF, influent and effluent twice a week grab samples have been collected and analysed for TKN, AN, BOD5, COD, TSS, Alkalinity, Total coliform, pH, DO and Temperature. Furthermore, slime samples from the VFASSF system has been collected for nitrifying bacteria identification using SEM microscope analyses. From optimization study, the optimum value of HLR and aeration rate was 2.72 m3/m3.d and 10 L/min, respectively and has been further investigated in the ASSF monitoring study using VFASSF and HFASSF system. From the second experiment, it was found that the VFASSF system has outperformed as the removal efficiency of TKN, AN, TSS, and Total coliform were 89%, 97%, 86%, and 97%. The removal efficiency was slightly lower in the HFASSF as their removal were 78%, 71%, 88%, and 91% for TKN, AN, TSS, and Total coliform. Throughout the study, DO profile in VFASSF effluent consistently higher than in HFASSF as the value average at 5.2 mg/L and 3.75 mg/L, respectively. In addition, identification study using SEM and microscope analysis, it was confirmed that nitrifiers were present in VFASSF system with in rod-shape. In conclusion, it was indicated that most of ammonia nitrogen were converted to nitrate-nitrogen through nitrification process in the highly aerated VFASSF system than HFASSF system. More than 95% of AN were converted to NO3-N in the system which is 18.65 mg/L where the limit is within in the permissible limit of Standard B which is 50 mg/L.