The in fl uence of hydraulic loading on bio fi lm properties in a subsurface wastewater in fi ltration system

Rapid urbanization and population growth in China have contributed to environmental pollution, which includes surface water eutrophication. Landscape water, a form of surface water, can beautify the environment, increase humidity, clean the atmosphere, improve a district’s local climate, and enhance people’s appreciation for the environment. With the rapid economic development of China, nitrogen and phosphorus lead to serious eutrophication of urban landscape waters. Treating this landscape water is critical to both the environment and quality of life. A subsurface wastewater infi ltration system (SWIS) has been used to successfully treat landscape water with low-concentration pollution (Yang et al. 2010, Zhang et al. 2011). A SWIS has many advantages, such as simple construction, low operational and maintenance costs, and simple operation (Avinash et al. 2009, Belinda et al . 2007, Pan et al. 2013). In a SWIS, wastewater is first treated using conventional physico-chemical or biological methods; the water then permeates an aerated unsaturated zone, where it is purified using processes such as filtration, adsorption, chemical reaction, and biodegradation (Li et al. 2012). A fundamental characteristic of a SWIS is that its functionality relies heavily on the metabolism of microorganisms contained within the biofi lm. As such, studying the biofi lm treatment process and characteristics, such as biofi lm weight, activity and spatial distribution, are an important part of SWIS studies and may help improve SWIS structure. Microbial ecology studies broaden knowledge about microbial communities and may help improve SWIS design and performance by providing effective indicators of biofilm function and health. Lazarova and Man em (1995) reviewed the techniques used to measure biofi lm activities and characteristics, and concluded that simple and precise methods to measure bacterial biomass and activity are needed to maximize biofi lm benefi ts. As the indicators of biofi lm development and activity, a range of parameters, such as VSS (volatile suspended solid), viable cells numb er, protein, polysaccharide, respiration intensity and dehydrogenase activity (electron transport system activity), can be used to describe biofi lm weight and activity in SWIS. To a certain extent, VSS expresses the quantity of the bi ofi lm. Viable cells can be express by viable biomass in biofi lm system, which can be quantifi ed using phospholipids extraction and phosphate analysis (Findlay et al. 1989). The physico-chemical properties of carrier surfaces induce bacterial cells to secrete extracellular polymeric substances (EPS), when these cells are deposited onto fi llers (Renner and Weibel 2011). EPS are high-molecular-weight molecules consisting of polysaccharides, DNA, proteins, lipids, and humic acids. These molecules are released by microbes and adhere onto the cell surfaces of activated sludge, granular sludge, and biofi lms in wastewater treatment plants (Flemming and Wing ender 2010). As the main components of EPS, protein and polysaccharides produced by growing bacteria indicate Archives of Environmental Protection Vol. 42 no. 4 pp. 70–79 PL ISSN 2083-4772 DOI 10.1515/aep-2016-0044