# Removal of Volatile Solids from Greywater Using Sand Filters
## 1 Introduction  
With shrinking resources and rising costs of water treatment (for example in sand filter), the reusability of water is technologically and economically justified. According to the literature, greywater, which has a lower sanitary hazard than domestic sewage, is acceptable for research and implementation [1, 2]. Population growth, industrialization, and climate change have resulted in worldwide scarcity of fresh water. This is not limited to arid or semi-arid regions, but has also surfaced in many countries in Asia, South Africa, and southern Europe [3, 4]. In addition, half of the population in India and China is facing water shortage [5] and two-thirds of the world's population will face some sort of water stress by 2025 [6]. This shortage has promoted interest in finding an alternative source of water. Greywater, thus emerges, because it can be treated for non-potable reuse, such as flushing of toilets, irrigation, and washing, saving up to 30-60% of household water consumption [7, 8]. Greywater, defined as wastewater generated from washing basins, baths and showers, washing machines, and the kitchen, accounts for 50-80% of the total volume of household wastewater [9, 8]. Low-load greywater, which excludes kitchen sources, was found to be responsible for up to 70-75% of the total domestic wastewater volume, and shows feasibility for treatment and reuse because of its characteristics and composition [10, 11]. The amount of greywater generated per person varies among countries and territories, and is dependent on several factors, e.g. 70-140 dm\({}^{3}\)/person in developed countries, 127-151 dm\({}^{3}\)/person in the United States, and 20-30 dm\({}^{3}\)/person in developing countries [12, 13, 14]. Greywater contains products such as soap, shampoo, shower gel, powders, skin, hair, and pathogens,which are a result of human activities. However, the concentration of organic pollutants and nitrogen compounds in greywater is lower than that in household wastewater [7]. The particle size of greywater is in the range of 10-100 \(\upmu\)m [15]. Moreover, the physicochemical characteristics of greywater depend on the quality of water supply, lifestyle, activities of people, material of the water supply pipe, household products used, and other factors [10]. Organic matter (soluble and particles) in greywater is an important parameter that helps assess the quality of treatment for reuse, owing to its potential risk to air, soil and plants [16]. 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]. However, the efficiency of removal varies and depends on many factors--particle size, hydraulic loading rate, and height of the sand layer, among others. In addition, [PERSON] et al. [11], in their study, concluded that a biofilm is formed on the sand filter, thus enhancing COD removal. Furthermore, the mean mass of organic matter in samples of filter sand was found to be basic for developing biofilms [11]. 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. Slow down-flow sand filtration has low treatment efficiency, but is useful as a primary treatment stage for greywater reuse, due to its construction simplicity and ease of washing (most frequently by backwashing). Due to the relatively low cost of tap water in Poland (about 2-3 EUR m\({}^{-3}\)), there is the need for easy and cheap solutions.