Comparative Evaluation of Activated Carbon and Granulated Blast Furnace Slag in Treating Greywater

Abstract

Recycling greywater (GW) for on-site, non-potable application can reduce the load to wastewater treatment plants and stress on potable water demand for domestic water supply. However, utilization of GW requires careful treatment to ensure reduction of all contaminants to acceptable level. The conventional methods for GW treatment are expensive and energy intensive. Consequently, the search for efficient and cost-effective treatment has been on a rise in recent decades. This study investigates the effectiveness of granulated blast furnace slag (GBFS) and activated carbon (AC) in the treatment of GW from a residential building in Sharjah, United Arab Emirates. GBFS is a by product formed during the production of iron and steel-making. Since GBFS is commonly considered a waste, its utilization allows for waste reduction. Six configurations, each having a different combination of filter media, adsorbent, ultra-violet (UV) radiation and chlorine disinfection were setup at a pilot scale to assess (i) effectiveness of AC and GBFS in treating GW (ii) the impact of pre-treatment on treated water quality and (iii) the efficiency of UV and chlorine disinfection in microbial reduction. Results demonstrated that GBFS achieved higher or comparable removal efficiency for turbidity (90 – 92 %), BOD5 (76 – 86 %), COD (64.6 – 85.1 %), TSS (66.8 – 88.5 %) and TOC (80.6 – 92.7 %) in contrast to AC. GBFS displayed lower TDS removal (0 – 26 %) in contrast to AC (35.8 – 55.4 %). The addition of filter media prior to GBFS enhanced removal of TOC by 1- 3mg/l, TSS up to 99.1 % and turbidity up to 92.1 %. GBFS displayed higher reduction of TC (0.54 – 2.05 log removal) and FC (1.96 – 2.30 log removal) in contrast to AC. UV efficiency in FC and TC reduction varied in the range of 2.5 – 4.4 log removal and 0.4 – 2.7 log removal, respectively. Finally, human risk reduction performed on TC displayed GBFS combined with pre-treatment achieved lower hazard quotient (HQ) values, thereby producing reclaimed water of lower risk in comparison to AC. The study proved that it is possible to introduce GBFS as a sustainable alternative to conventional AC adsorbent for treatment of greywater at household level for non-potable use.