Greywater treatment by slanted soil system
Introduction
Naked dry soil with no plant is difficult to keep rich soil ecosystem and it can be easily lost by wind or rain erosion. This kind of soil deterioration has considerable effect on ecosystem and agricultural productivity in arid or semi-arid zone (Lal, 1998, Visser et al., 2005). Planting through a year can reduce this soil deterioration; however, water limitation does not allow it in these areas. For example, in rural area of Burkina Faso, which belongs to semi-arid zone, farmers can cultivate their main farmland only during rainy season. Only small garden which located in shoreline of reservoir or near the well, are able to be cultivated in dry season (Ushijima et al., 2012). Distribution and time periods of available water greatly affect the agricultural activity in this area, and most farmers are facing poverty problem due to such low productivity. On the other hand, people in this area use some amount of water for daily life even in dry season, and its wastewater is just disposed (Ushijima et al., 2012). Effective wastewater reuse has a potential to increase the cultivatable area and season, and it provides not only reduction of soil deterioration but also increase of productivity.
The concept of onsite wastewater differentiable treatment system (Lopez Zavala et al., 2002) can be one of suitable system for above-mentioned situation. It proposes onsite treatment of greywater, urine and feces separately, in order to achieve effective resource recycling system. Separated greywater has low concentration of pollutant load (Gajurel et al., 2003) and its treatment would be easier than mixed wastewater. For example, WHO (2006) wastewater reuse guideline stated that 2–7 log10 pathogen reduction by treatment is required for irrigation use, however separated greywater contains 2 log10 or more lower bacterial pathogen than mixed wastewater which WHO assumed (Ottoson and Stenström, 2003) and therefore we are able to set 5 log10 as a target level of bacterial pathogen reduction for separated greywater treatment. Furthermore, if reuse purpose was focused on irrigation only, advanced treatment technology for nitrogen, phosphorus removal would not be necessary. The most important point is to be low cost and simple, because most of those who need greywater reuse are low income people.
The slanted soil system is one of the promising treatment systems for this concept. It consists of several chambers containing soil (Fig. 1). These chambers are able to be stacked vertically, therefore its footprint is very small (e.g. approximately 1.0 m × 0.5 m). This system accepts direct discharge of greywater (Kondo et al., 2011) therefore no pump and no septic tank are required. Itayama et al. (2006) and Kondo et al. (2011) performed continuous monitoring of slanted soil system used by real household in Japan. Itayama et al. (2006) reported averaged removal ratio of the COD, the SS, the TN and the TP as 85%, 78%, 78% and 86%. Li et al. (2009) referred this result and concluded that the treated water is not suitable for reuse because it remains high in organic load and suspended solids, which can limit the chemical disinfection. These are however not the discussion for irrigation use but for avoiding eutrophication (Itayama et al., 2006) or for potable reuse (Li et al., 2009). Therefore, in this study, we evaluated the performance of the slanted soil system as a treatment facility for irrigation reuse, and proposed its design criteria for arid or semi-arid zone.
Section snippets
Experimental apparatus and operation
Full scale slanted soil system was installed inside of laboratory; four soil chambers were connected as shown in Fig. 2, the size of each chamber was 0.10 m of depth, 0.145 m of width, and 0.94 m of length, chamber bed has gradient of 1/20. We performed 6 cases of experiments, in variety of soil type, soil particle size and amount of discharged wastewater (Table 1). In all experiments, greywater was discharged to first chamber 3 times in a day because actual discharge pattern of greywater shows 2
SS removal and clogging
SS removal by treatment length was almost linear in logarithmic graph (Fig. 3). Total removal rates through 4 chambers were 60–94%, and these were higher in finer particle and lower discharge (Fig. 4). Discharged water was overflowed from the chamber due to clogging in Cases 3, 4, 5 and 6 at the 5th, 3rd, 8th and 3rd week, respectively. Time periods until clogging (T) were longer in coarser soil and higher discharge. In Case 5, combination of fine and coarse soil, T was longer than those using
Treatment performance
Fine soil presented better removal performance of pathogen, SS, and T-COD. Particularly, sufficient pathogen removals were performed only by fine soil chamber, while most part of pathogen passed through coarse soil chamber. Disadvantage of fine soil was shorter time periods until clog, however result of Case 5 represented that combination of coarse and fine soil can extend this time period to more than double. Most of previous studies used Kanuma soil, which is generally 10 mm or larger particle
Conclusions
Performance of the slanted soil system for greywater was evaluated in light of required water quality for irrigation reuse. The slanted soil system performed high removal rate in both P-COD (94–97%) and BDOC (88–89%), while removal rate of D-COD (58–68%) was comparatively low. LAS removal rates were more than 90% and final concentrations (2.3–3.3 mg L−1) were sufficiently lower than 8 mg L−1 which was proposed as target level for irrigation use (Hijikata et al., 2011). First order reaction equation
Acknowledgements
This research was supported by JST-CREST, JST-JICA and JSPS-Science Research (type S).
References (20)
- et al.
Review of the technological approaches for grey water treatment and reuses
Sci. Total Environ.
(2009) - et al.
Bacterial dynamics in the drinking water distribution system of brussels
Water Res.
(2001) - et al.
Faecal contamination of greywater and associated microbial risks
Water Res.
(2003) - et al.
Nutrient losses by wind and water measurements and modelling
Catena
(2005) Bacteriophages
(1959)Standard Method for the Environment of Water and Wastewater
(1985)- et al.
Fractioning gray-water in the differentiable onsite-wastewater treatment system
- et al.
Investigation of the effectiveness of source control sanitation concepts including pre-treatment with Rottebehaelter
Water Sci. Technol.
(2003) - et al.
Phytotoxicity assay of several gray waters for reuse as agricultural irrigation
- Huelgas, A.P., 2009. Onsite Treatment of Higher-load Graywater by Membrane Bioreactor. Dissertation for the doctoral...
Cited by (34)
Application of downflow hanging sponge reactor and biochar for water and wastewater treatment
2022, Current Developments in Biotechnology and Bioengineering: Advances in Biological Wastewater Treatment SystemsPerformance and treatment assessment of a pilot-scale decentralized greywater reuse system in rural schools of north-central Chile
2022, Ecological EngineeringCitation Excerpt :The type of technology developed and used in different parts of the world strongly depends on the income level of each country. In some sub-Saharan African countries, the implementation of low-cost treatment systems, such as filtration using a slanted soil system, has been studied (Maiga et al., 2014; Ushijima et al., 2013). Countries with more experience in the reuse of greywaters, such as Japan or Australia, use more sophisticated treatment systems based on biological reactors for the remediation of greywater, which are commercialized by specialized companies (Cecconet et al., 2019; Fountoulakis et al., 2016; Watanabe et al., 1993; Yoshikawa et al., 2019).
Life cycle assessment of greywater treatment systems for water-reuse management in rural areas
2021, Science of the Total EnvironmentCitation Excerpt :Greywater is distinguished into light greywater from showers and washbasin; and dark greywater from laundry and kitchen which include waters with higher organic matter (Albalawneh and Chang, 2015). Some previous studies show the potential benefit of the treatment and reuse of greywater (Al-Wabel, 2011; Maiga et al., 2014; Ushijima et al., 2013; Yoshikawa et al., 2019). The amount of greywater generated by a home varies depending on the lifestyle, however, it generally ranges between 50 and 80% of the total water consumption at the household level (Al-Gheethi et al., 2019).
Effective control of waterborne pathogens by aquatic plants
2020, Waterborne Pathogens: Detection and TreatmentConstructed wetland for wastewater reuse: Role and efficiency in removing enteric pathogens
2019, Journal of Environmental ManagementCitation Excerpt :Likewise, Bohórquez et al. (2017) observed better elimination TC and EC in the vertical flow CW filled with sand (1.2–2.7 and 1.5–3.5 log units removal respectively) compared to those with gravel media (0.00–0.08 log units removal) (Bohórquez et al., 2017). Ushijima et al. (2013) reported a reduction of 5 logs and 3 log units for E. coli and MS2 phage, respectively by using fine soil as a substrate in horizontal subsurface flow CW, whereas coarse soil failed to remove these microorganisms (Ushijima et al., 2013). According to Cui et al. (2010), the grain size of the filter media or substrate is one of the determining factors of removal efficacy, since the smaller size of grain provides larger specific surface area for various interactions (Cui et al., 2010).
Enhanced treatment of greywater using electrocoagulation/ozonation: Investigation of process parameters
2019, Process Safety and Environmental ProtectionCitation Excerpt :The GW quality and quantity depend on the lifestyle in the household, income of households, water quality, and the choice of cleaning chemicals used during washing-up, laundry and in the shower (Ahmadi and Ghanbari, 2016; Boyjoo et al., 2013; Li et al., 2009). Some conventional treatment processes have been used for GW treatment which are applied for the removal of total suspended solids (TSS) and organic carbon (Chong et al., 2015; Ushijima et al., 2013). Most of them have been designed to achieve the regulation and requirements of non-potable greywater reuse such irrigation and toilet flushing.