Treatment efficiency and recovery in sand filters for on-site wastewater treatment: Column studies and reactive modelling

• Published in: Journal of cleaner production 2024-07, Vol.462, p.142696, Article 142696
• Main Authors: Hamisi, Rajabu, Renman, Agnieszka, Renman, Gunno, Wörman, Anders, Thunvik, Roger
• Format: Article
• Language: English
• Subjects: Adsorption; Nitrogen; Optimization; Phosphorus; Reactive transport modelling; Tidal flow constructed wetland
• ISSN: 0959-6526; 1879-1786
• DOI: 10.1016/j.jclepro.2024.142696

This study examined the adsorption capacity and treatment efficiency of sand filters in on-site treatment systems for cold climate regions. The effects of different operating conditions, porosity and kinetics parameters were investigated in column experiments and COMSOL Multiphysics® modelling, to comprehensively reveal the mechanisms and optimize treatment efficiency of nitrogen (N) and phosphorus (P) removal in a field tidal flow constructed wetland (TFCW), treating effluent from a package treatment plant with P filter material. The results from column experiments with sand showed that Total-P adsorption rate was dependent on feed water quality (Septic tank >0.77 ± 0.06 g kg−1; Biotreatment >0.41 ± 0.07 g kg−1; Reactive material Polonite® 1.42 ± 0.55 g kg−1) and middle layer (>1.06 ± 0.51 g kg−1) was twice that in laboratory columns, due to strong interaction with the air-water interface and use of fluctuated domestic wastewater solutions. The breakthrough curve (BTCs) of the coarse sand matched the physical behaviour of tracer electrical conductivity (EC) in effluent from the sand column experiments. The modelling results demonstrated that high filter porosity and low hydraulic load were significant factors for optimal removal of NH4–N, Total-N, PO4–P, Total- P in the top layer (>99.95 ± 0.03 %, 44.37 ± 28.75%, 70.89 ± 28.30%, 76.18 ± 20.3%), middle layer (>98.94 ± 1.77%, 18.23 ± 23.04%, 76.62 ± 28.73%, 65.40 ± 31.85%) and deep layer (>99.99 ± 0.02%, 65.50 ± 20.64%, 75.53 ± 23.16%, 41.54 ± 28.81%) in the TFCW system, respectively. The results show that on-site wastewater treatment in cold climate TFCW can be applied as a technology to polish effluent from a three-step pretreatment system. However, hydraulic optimization is an important factor for the design of the TFCW to receive a successful long-term operating system. [Display omitted] •Treatment efficiency of the sand filters were studied using column experiemnts and reactive COMSOL Multiphysics® modelling.•Organic matter in the influent wastewater solution increased phosphorus (P) storage capacity of the sand filters.•The downflow influent slightly increased P adsorption capacities than the upflow influent.•Breakthrough curves of the coarse sand matched the physical behaviour of the tracer EC in effluent from column experiments.•COMSOL modelling generated new insights into dynamic mechanisms of water flow and nutrie