Effect of mixing Nano-silica and Perlite with pervious concrete for nitrate removal from the contaminated water

Abstract

Nitrogen and phosphorus contained in storm water runoff contaminate both surface and ground waters, causing problems for natural aquatic systems and human health. Pervious concrete particularly developed for pollutant removal might be a novel notion to remove nitrate from runoff. In this research, three aggregates were used in pervious concrete as Nano silica, perlite (Pe) and zeolite (Z) which are able to adsorb pollutants. The water absorption, compressive strength, porosity, permeability of aggregate and nitrate removal of concrete samples were evaluated in tests. While adding Nano silica, perlite and zeolite, experiments have shown that addition of fine grains enhances runoff efficiency and compressive strength, but reduces permeability and porosity. Both adsorbents improved the runoff quality while increasing the additives' ratio. The mechanical properties were density of 879 (Kg/m3), permeability of 1.06 (cm/s), the void rate of 19.7(%), compressive strength of 3.6 (MPa), and nitrate removal of about 75%. While adding perlite with the highest (40%) water absorption, the results showed no reactivity of aggregates in terms of alkali-silica reaction. Considering the Permeability tests, perlite has the minimum (1.4 cm/s) permeability, and then adding perlite to previous concrete brought the nitrate absorption capacity about 70 ml/g (60%). The best results belonged to samples containing zeolite treatments (with 15% adsorbent and 0, 10, 20% fine-grains) with a maximum pollution decline and improved Chemical Oxygen Demand (COD) (87.1, 82.6 and 89.3%), Biochemical oxygen demand (BOD) (88.1, 87.3 and 90.7%) and Total suspended solids (TSS) (75.8, 79.1 and 84.6%). Thus, zeolite has shown effective mechanical characteristics and runoff quality, while perlite and Nano silica has shown a poor and moderate performance among the adsorbents in all tests, respectively.