Implications of the operation of continuous granular activated carbon filters on the effluent quality

Abstract

Granular activated carbon (GAC) filtration is a commonly used method for advanced wastewater treatment. Filters can be operated continuously or discontinuously, with continuous operation not requiring feed flow interruption for backwashing and circulation (B/C). This study investigated the influence of B/C on the effluent quality of continuous filters. Two continuous GAC filters were operated for 1.5 years, with analysis of dissolved substances and particulate matter in the influent and effluent. The results indicated that various B/C modes had no impact on the removal of dissolved organic carbon and organic micropollutants (OMP), achieving an OMP removal of over 70% after 5,600 treated bed volumes (m3 treated wastewater per m3 GAC). However, it was evident that continuous B/C over 2–4 h resulted in increased turbidity, total suspended solids over 30 mg/L and total phosphorus concentrations of 1.3 mg/L in the filter effluent. Additionally, the study demonstrated that longer and more intensive B/C processes resulted in GAC size degradation with AC concentrations of up to 6.9 mg/L in the filter effluent, along with a change in GAC particle size. Furthermore, the importance of pre-filtration in reducing particulate matter in the filter influent and decreasing hydraulic head loss could be demonstrated. HIGHLIGHTS Operation of two continuous granular activated carbon (GAC) filters.; Different backwashing and circulation (B/C) modes were investigated.; Dissolved substances removal (DOC and micropollutants) showed no dependence on B/C mode.; Intensive and long-lasting B/C resulted in GAC abrasion and increased particulate matter and activated carbon concentration in filter effluent.; Pre-filtration was necessary for filter operation.;

Keywords

• adsorption
• dissolved organic carbon
• gac degradation
• residual activated carbon concentration
• total phosphorus
• total suspended solids