Efficiency of Private Household Sand Filters in Removing Nutrients and Microbes from Wastewater in Finland

Abstract

Sand filters have been shown to be an economic and effective solution for wastewater treatment in private households, although the removal of phosphorus (P) may be insufficient. However, P removal can be improved by adding a P-adsorbing material, such as biotite, into the sand filters. The physico-chemical characteristics and the microbial quality of the effluents of family-scale sand filters without adsorbing media (SF), sand filters with a biotite layer (B), and sand filters with a modular filter (MB) were followed for one year. Sand filters with a biotite layer displayed the highest capacity to remove nitrogen (N) and biological oxygen demand BOD 7 . The efficiency of these filters did not depend on the age of the filter or the season. The P load of the effluent did not differ between sand filters with and without a biotite layer, but the modular sand filter failed to adequately reduce P. The treatment efficiency of sand filters without biotite decreased with increasing age. These private household sand filters can be a good way to treat domestic wastewaters, since these generally comply with the minimum requirements of a Finnish Decree (157/2017). However, enteric viruses (noroand adenoviruses) were commonly found in the effluents, and the numbers of Escherichia coli were often above 10 3 colony forming units (CFU) 100 mL −1 (limit for the the EU Bathing Water Directive 2006/7/EC) for good water quality), signifying a risk of microbial contamination of nearby drinking water wells, as well as bathing and irrigation waters.

Removal of Volatile Solids from Greywater Using Sand Filters

“…Removal efficiency of organic compounds in this study (26.8%) was similar to that obtained by Alsulaili [45] (17%) and Moges et al [46] (20-25%), and also comparable to results obtained by Santos et al [44] in a study carried out using a filter mesh of 0.130 mm diameter (47%). COD removal efficiency was much lower than the removal efficiency obtained by other authors: Martikainen et al [18]-for conventional buried sand filters (92%), and Abdel-Shafy et al [17]-for a down-flow gravel filter (74%). Higher removal efficiency than this study was obtained by Khalaphallah [47] for commercial sand used in the filtration of swimming pools-55%.…”

“…Sand filters have been studied and applied in greywater treatment; they offer a common, low-cost technology with easy operation and maintenance, and efficient removal of total suspended solids (TSS) [17,18]. Several studies have shown that sand filters efficiently remove COD and TSS [11,16,17].…”

“…Sand filters are becoming popular and have been achieving economic efficiency in greywater treatment for reuse in households and for irrigation in regions of water shortage [18,19]. Sand filters that are used in greywater treatment need more attention, as there is a lack of research on clogging time, distribution of organic matter in the vertical column of the sand filter (potential for formation of biofilm), and loading treatment.…”

“…So far, mainly conventional technologies and constructions have been investigated and used on a technical scale [18]. There are several literature reports that describe modified or alternative systems [35].…”

The impact of biodegradable carbon sources on microbial clogging of vertical up-flow sand filters treating inorganic nitrogen wastewater

“…Clog matter can considerably reduce pore spaces in the granular medium because of its lower density (Knowles et al, 2011). Clogging is often initiated in the top zone of the main filter layer, where abundant biological growth can occur due to contact between the fine media, nutrients, and organic matter in the influent wastewater (Martikainen et al, 2018). Gajewska (2013) reported that bed clogging is influenced by organic matter accumulation.…”