Combined Vertical-Horizontal Flow Biochar Filter for Onsite Wastewater Treatment—Removal of Organic Matter, Nitrogen and Pathogens

Sahar S Dalahmeh,Almoayied Assayed,Ylva Stenström

doi:10.3390/app9245386

Sahar S Dalahmeh, Almoayied Assayed + Show 1 more

Open Access

https://doi.org/10.3390/app9245386

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Abstract

This study investigated the performance of a combined vertical-horizontal flow biochar filter (VFF-HFF) system in terms of organic matter, total nitrogen (Tot-N), Escherichia coli and Salmonella removal and explored the effects of hydraulic loading rate (HLR) on pollutant removal. The combined VFF-HFF system used biochar as the filter medium and comprised two stacked sections: (i) an aerobic vertical flow filter (VFF) in which the wastewater percolated through the biochar medium in unsaturated mode and (ii) a horizontal flow filter (HFF), in which the biochar was saturated with water and had limited access to air, to enable anaerobic conditions and enhance the denitrification process. The system was tested over 126 weeks using real wastewater applied at different HLR (23, 31, 39 L m−2 day−1). The results showed that long-term removal of organic matter in the entire system was 93 ± 3%, with most (87 ± 5%) occurring in the VFF. For Tot-N, the long-term removal was 71 ± 12%, with increasing trends for nitrification in the VFF and denitrification in the HFF. Mean long-term nitrification efficiency in the VFF was 65 ± 15% and mean long-term denitrification efficiency in the HFF 49 ± 14%. Increasing HLR from 23 to 31 L m−2 day−1 increased the nitrification efficiency from 42 to 61%. Increasing the HLR further to 39 L m−2 day−1 decreased the denitrification efficiency from 45 to 25%. HLR had no significant effects on VFF and HFF performance in terms of E. coli and Salmonella removal, although the VFF achieved a 1.09–2.1 log10 unit reduction and the HFF achieved a 2.48–3.39 log10 unit reduction. Thus, long-term performance, i.e., removal of pollutants measured during the last 52 weeks of the experiment, was satisfactory in terms of organic matter and nitrogen removal, with no signs of clogging, indicating good robustness of the combined VFF-HFF biochar filter system.

Highlights

Biochar is a carbon produced by thermal decomposition of organic materials at elevated temperature (300–800 ◦ C) in the absence of oxygen [1]
hydraulic loading rate (HLR) had no significant effects on vertical flow filter (VFF) and horizontal flow filter (HFF) performance in terms of E. coli and Salmonella removal, the VFF achieved a 1.09–2.1 log10 unit reduction and the HFF achieved a 2.48–3.39 log10 unit reduction
Over the whole experimental period (126 weeks), the average concentration of chemical oxygen demand (COD) applied to the system was 144 ± 171 mg L−1 in the VFF and 39 ± 33 mg L−1 in the HFF (Figure 2)

Summary

Introduction

Biochar is a carbon produced by thermal decomposition of organic materials at elevated temperature (300–800 ◦ C) in the absence of oxygen [1]. In the wastewater treatment sector, there is growing interest in using biochar as a renewable biofilm carrier and adsorbent to replace or complement sand filters. This is because utilization of biochar for wastewater purification increases treatment efficiency and reduces the spread of hazardous contaminants, and helps to conserve finite natural sands and mountain landscapes and to mitigate climate change effects through carbon sequestration [2,3].

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