Municipal Wastewater pretreatment using porous concrete containing fine-grained mineral adsorbents

Abstract

Municipal and industrial wastewaters are serious threats for surface water and groundwater resources, and this threat can be converted to an opportunity by enhancing their quality, which then can be used for agricultural and landscape purposes. In the present study, the performance of porous concrete (PC) containing mineral adsorbents was investigated to improve the municipal wastewater quality. Firstly, the performance of adding fine grains (2.36–4.75 mm) in different portions (0, 10, and 20 % w/w of coarse aggregates) as well as mineral adsorbents (0.6–1.2 mm), namely zeolite, pumice, perlite, and LECA, in different portions (0, 5, 10 and 15 % w/w of coarse aggregates) on compressive strength, porosity and permeability coefficient of porous concrete was pursued. After evaluating these parameters, three samples from each percentage of fine-grains that had the highest compressive strength were selected for wastewater qualitative tests due to the fact that there was no significant difference between the other two factors. The experimental setup was next to the wastewater treatment plant of Semnan University, Semnan, Iran, which included a 200-L barrel and six canals to perform the quality tests. Six 100 × 100 × 100 mm PC specimens were positioned in each canal, in a zigzag pattern, to slow down the wastewater flow through the specimens. Inlet discharge for each canal was fixed at 0.5 L/min and total test time was 31.2 h. Qualitative parameters such as total suspended solids (TSS), chemical oxygen demand (COD), biochemical oxygen demand (BOD), and turbidity were measured before and after running the experiment. Results revealed that adding fine grains and the adsorbents increased the compressive strength, while they reduced the permeability coefficient and porosity. Also, the specimens containing zeolite and pumice had the highest compressive strength and permeability coefficient, respectively. Furthermore, mineral adsorbents reduced average concentration of TSS, BOD and COD by 40 %, 48 % and 30.5 %, respectively. The only factor that affected average turbidity level (49 NTU) was porosity, and not the mineral adsorbents. Finally, zeolite had the highest physical characteristics as well as high pollutant-reduction potential. However, it is recommended to perform further tests on different porous concrete mixtures and other adsorbents.