On-site Domestic Wastewater Treatment Systems Research Articles

［Joint Seminar by Younger Researcher's Associations at JSMCWM and SECE］ Design of Onsite Domestic Wastewater Treatment Systems toward Decarbonization

［Joint Seminar by Younger Researcher's Associations at JSMCWM and SECE］ Design of Onsite Domestic Wastewater Treatment Systems toward Decarbonization

Environmental assessment of on-site source-separated wastewater treatment and reuse systems for resource recovery in a sustainable sanitation view

Sustainable sanitation solutions are necessary for promoting public health and environmental security. In this study, on-site domestic wastewater treatment (WWT) systems used for households in rural and peri-urban areas of Brazil were compared in different scenarios from a life cycle assessment (LCA) perspective. The evaluated scenarios represented different practices in wastewater management, such as direct discharge into the soil, rudimentary treatment, septic tank, public sewerage system, and source separation of wastewater streams for water, nutrient, and organic matter recovery. The WWT technologies considered in the proposed scenarios of source-separated wastewater streams were as follows: an evapotranspiration tank (TEvap) and composting toilet for blackwater, a modified constructed wetland (EvaTAC) for greywater, and a storage tank for urine. LCA was performed in this study according to the ISO standards to assess the environmental impacts at both midpoint and endpoint levels. The results show that on-site source-separated wastewater treatment systems with resource recovery result in significant reductions in environmental impacts compared to scenarios with precarious conditions or ‘end-of-pipe’ solutions. For example, regarding the human health damage category, the scenarios involving resource recovery, including systems such as EvaTAC, TEvap, composting toilet, and urine storage tank, demonstrate significantly lower values (−0.0117 to −0.0115 DALY) compared to scenarios with rudimentary cesspits and septic tanks (0.0003 to 0.001 DALY). We conclude that the focus should be beyond mere pollution aspects and instead concentrate on the benefits of the co-products, which are: avoiding the extraction and consumption of valuable and increasingly scarce raw materials, such as potable water, and production of synthetic fertilizer. Furthermore, it is highly recommended that an LCA of sanitation systems synergistically integrates the WWT process, the constructive aspects, and the resource recovery potential.

Sludge accumulation rates in septic tanks used as part of the on-site treatment of domestic wastewater in a northern maritime temperate climate

On-site domestic wastewater treatment systems (DWTS) are used by a significant fraction of the world's population and are used by one third of the population in Ireland. The effective operation of these DWTS requires regular desludging and so knowledge of expected filling rates is essential for both the homeowner as well as the municipalities which accept this sludge in licensed premises; yet few studies have attempted to quantify the sludge accumulation in such decentralized systems. Field studies were carried out on 27 septic tanks across Ireland to quantify sludge accumulation rates from which optimum desludging frequencies for use in Ireland have then been determined. Sludge accumulation was found to be very high in the first 12 months of system operation (approximately 250 L/person/y) but dropped off to below 150 L/person/y after 2 years. Such volumetric accumulation rates appear high compared to the few other reported international studies; however, measured solids accumulation rates, were low compared to international estimates, ranging from 1 to 10 kg/person/y. An equation for optimal desludging frequencies between 3 and 5 years has been formulated for various tank sizes and occupancy based on the Irish field data and previous international research - 5 years being the maximum allowable interval between desludging before the limiting volume of 50% sludge in the tank is reached.

A Simple Method for Identifying Appropriate Areas for Onsite Wastewater Treatment

Onsite Domestic Wastewater Treatment Systems (ODWTS) are increasingly important for treating domestic wastewater in metropolitan contexts, especially in suburban sectors isolated from sewer networks and centralized treatment plants. When ODWTS are not correctly planned and located in suitable places, or are not properly designed, they can cause groundwater contamination and generate risks for human health. This work presents a Spatial Decision Support System (SDSS) to zone specific areas based on a few simple parameters. The proposed tool can be easily adapted to different contexts, even where institutional capacities are low. Results obtained in the metropolitan area of the Lerma Valley (Salta, Argentina) show strong contradictions between our zoning and current urbanization features in the study area. As a result, environmental impacts and health hazards are likely to manifest in the short or medium term. The sectors with the best receptivity conditions were found in the southern sector of the study area. We argue that ODWTS can be safely implemented in many areas as long as this concept is embedded in urban planning initiatives, which usually also require the consolidation or development of appropriate institutions and control systems.

On-site domestic wastewater treatment system using shredded waste plastic bottles as biofilter media: Pilot-scale study on effluent standards in Bhutan

In this study, a 1000 L/d capacity one-off on-site wastewater treatment system was operated for over a year as a pilot alternative to the conventional on-site treatment as currently used in urban Bhutan. An up-flow anaerobic sludge blanket (UASB) was used for blackwater treatment (to replace “septic tank followed by an anaerobic biofilter (ABF) (to replace soak pits) for the treatment of a mixture of greywater and UASB effluent. Shredded waste plastic bottles were used as the novel biofilter media in the ABF. During a yearlong operation, the pilot system produced a final treated effluent from ABF with average BOD5 28 mg/L, COD 38 mg/L, TSS 85 mg/L and 5 log units of Escherichia coli. These effluents met three out of four of the national effluent discharge limits of Bhutan, but unsuccessful to meet the Escherichia coli standard over a yearlong operation. Further, process optimisation may enable more significant Escherichia coli removal. An economic analysis indicates that the total unit cost (capital and operating expenditures) of this alternative wastewater treatment system for more than 50 users range between USD 0.27–0.37/person/month comparable to USD 0.29–0.42/person/month for the current predominant on-site system, i.e., “septic tanks”. This pilot study, therefore, indicates that this wastewater treatment system using shredded waste plastic biofilter media has high potential to replace the current conventional treatment, i.e., “septic tanks”, which are often overloaded with greywater and discharging effluents which does not meet the national standards.

Engineered silver nanoparticle (Ag-NP) behaviour in domestic on-site wastewater treatment plants and in sewage sludge amended-soils

Untreated sludge from small-scale on-site domestic wastewater treatment systems (septic tanks) was spiked with 20, 60 and 100 nm silver nanoparticles (Ag-NPs) to investigate Ag-NP behaviour in these systems that are widely distributed in rural areas. In addition, the release of Ag-NPs from a previously spiked clay-rich loam reference soil (LUFA 2.4) was evaluated, in the presence and absence of untreated sludge, to simulate the common practice of sludge disposal by spreading on agricultural land. Single particle ICP-MS was used to determine Ag-NP size distribution and the results were compared with total Ag (Ag-NP and ionic) measured in acid digested samples. As documented previously for large municipal scale wastewater treatment plants, Ag-NPs are found to be overwhelmingly (~98%) retained in the sludge in these small-scale systems. The Ag-NP retention efficiency on the LUFA reference soil amended with sludge is approximately 10 times greater than that of LUFA soil alone (in the absence of sludge). For soil spiked with 60 nm Ag-NPs, the calculated average diameter of Ag-NPs in the supernatant, after 24 h was 45 ± 3 nm (dissolution rate 7.2E−06 mol/m2·h for 60 nm Ag-NP), smaller than that of supernatant from the combined sludge/soil system (52 ± 2 nm), indicating lower Ag-NP dissolution rates in the sludge-amended soil. This study provides new information about the leachability of Ag-NPs from septic tank sludge and suggests that the effluent and sludge from septic tanks are potential sources of both nano- and dissolved ionic-Ag to environmental waters.

Using coconut husks in a full-scale decentralized wastewater treatment system: The influence of an anaerobic filter on maintenance and operational conditions of a sand filter

The critical situation of domestic wastewater treatment in the rural areas of Brazil stimulates the development or improvement of on-site systems using cheap and sustainable materials that can be applied in small and isolated communities. Although this is an important theme, few real scale systems have been studied. This study investigated a full-scale on-site domestic wastewater treatment system composed of a septic tank, an anaerobic filter filled with green coconut husks (Cocos nucifera) and an intermittent sand filter. The experiment was conducted in a rural area located in the city of Campinas (Brazil) and the system was built to serve a small community. The quality of the effluent generated by this combination is in accordance with Brazilian and European legislation and even allows for its reuse in agricultural activities. The results also demonstrate the feasibility of using coconut husks in anaerobic filters, providing a new and more sustainable destination for this material, which is normally treated as solid waste. The combination was shown to be a viable technology for small communities.

Suitability of fluorescent whitening compounds (FWCs) as indicators of human faecal contamination from septic tanks in rural catchments

Rural river catchments are impacted by diffuse pollution sources from agricultural practices and on-site domestic wastewater treatment systems (DWWTS), mainly septic tanks. Methods that can distinguish between contamination sources will significantly increase water management efficiency as they will allow for the development and application of targeted remediation measures. Fluorescent whitening compounds (FWC), are used as optical brighteners in laundry detergents and enter the environment through the discharge of domestic wastewater effluents. Due to their human specific source and potential simple fluorometric measurement this represents a very attractive method to be used by state monitoring agencies.In this study the suitability of FWCs as chemical indicators for human faecal contamination has been investigated in rural Irish catchments. It was found that no quantitative measurements are possible for FWCs in natural waters when using simple fluorometric methods. Hence a simple presence/absence approach needs to be applied. The detectability of FWCs was quantified and found to decrease with higher organic matter content of the river water which has its own fluorescence. This enabled the establishment of equations to predict detection limits and assess the method's suitability for individual catchments based on organic matter concentrations. Furthermore a modified photodecay method is suggested that increases sensitivity of the technique by up to 59%. Applications at rural study sites found some removal of FWCs in percolation areas of DWWTSs but they were still detectable 40 cm below the infiltration depth. FWCs were also detected as distinguishable peaks in impacted streams where septic tank effluents have a high contribution to the river flow.

Preparation of a hybrid monolithic stationary phase with allylsulfonate for the rapid and simultaneous separation of cations in capillary ion chromatography.

A hybrid monolithic column with sulfonate functionality was successfully prepared for the simultaneous separation of common inorganic cations in ion-exchange chromatographic mode through a simple and easy single-step preparation method. The strong cation-exchange moieties were provided directly from allylsulfonate, which worked as an organic monomer in the single-step reaction. Inorganic cations (Li(+), Na(+), K(+), NH4(+), Cs(+), Rb(+), Mg(2+), Ca(2+), and Sr(2+)) were separated satisfactorily by using CuSO4 as the eluent with indirect UV detection. The allysulfonate hybrid monolith showed a better performance in terms of speed and pressure drop than the capillary packed column. The number of theoretical plates achieved was 19,017 plates/m (in the case of NH4(+) as the analyte). The relative standard deviations (n = 6) of both retention time and peak height were less than 1.96% for all the analyte cations. The allysulfonate hybrid monolithic column was successfully applied for the rapid and simultaneous separation of inorganic cations in groundwater and the effluent of onsite domestic wastewater treatment system.

Modified septic tank-anaerobic filter unit as a two-stage onsite domestic wastewater treatment system

This study demonstrates the performance evaluation of a uniquely designed two-stage system for onsite treatment of domestic wastewater. The system consisted of two upflow anaerobic bioreactors, a modified septic tank followed by an upflow anaerobic filter, accommodated within a single cylindrical unit. The system was started up without inoculation at 24 h hydraulic retention time (HRT). It achieved a steady-state condition after 120 days. The system was observed to be remarkably efficient in removing pollutants during steady-state condition with the average removal efficiency of 88.6±3.7% for chemical oxygen demand, 86.3±4.9% for biochemical oxygen demand and 91.2±9.7% for total suspended solids. The microbial analysis revealed a high reduction (>90%) capacity of the system for indicator organism and pathogens. It also showed a very good endurance against imposed hydraulic shock load. Tracer study showed that the flow pattern was close to plug flow reactor. Mean HRT was also found to be close to the designed value.

Diagnosis of domestic wastewater sand filters

On-site domestic wastewater treatment (ODWT) systems are receiving renewed interest due to their simplicity of implementation, affordability and efficiency. The most widespread ODWT system is the sand filter with vertical drained flow (SFVDF). To optimise the design and maintenance of SFVDFs, it is important to be able to check the conformity of the installations, judge their treatment performance in service and estimate possible evolution and life expectancy. As yet, however, no methodology has been developed to perform these tasks. This paper proposes a new methodology for diagnosing SFVDF systems in service. The development of this methodology relies on the development of on-site characterisation of the filtering material based on the use of a light dynamic penetration test and image processing. From this, the paper proposes an automatic tool for detecting the presence of clogging in a filter and a methodology to estimate the hydraulic conductivity of the filtering material without destroying the filter. The global methodology for diagnosing SFVDF systems is presented and illustrated for a real case in order to demonstrate its advantages and efficiency.

Cold Climate Performance Analysis of On-Site Domestic Wastewater Treatment Systems

Household on-site septic systems with secondary wastewater treatment in Anchorage, Alaska, were sampled and analyzed for performance parameters during the winter to spring months. System types included intermittent dosing sand filters (ISF), three types of recirculating trickling filters (RTF), and suspended-growth aeration tanks. Total nitrogen from the trickling filter and aeration tank effluent was fairly uniform, at approximately 30 mg/L. Total suspended solids (TSS) means were mostly less than 15 mg/L. The 5-day biochemical oxygen demand (BODs) showed considerable variability, with means ranging from 9.2 mg/ L for ISFs up to 39.5 mg/L for one type of RTF, even though this type has shown excellent results in several test programs. The data suggested that effluent temperature within the sample range had almost no effect on effluent concentrations of BOD5 or TSS and only a small effect on the removal of total nitrogen. Non-climatic factors were probably of equal importance to treatment results.

Natural Attenuation of Endocrine Disrupting Chemicals in On-Site Domestic Wastewater Treatment Systems

Abstract Groundwater is an important resource in Ireland which is under increasing risk from the burgeoning numbers of decentralized houses and their respective on-site treatment systems which discharge effluent to ground via a number of parallel percolation trenches. The three-dimensional performance of separate percolation areas have been intensively monitored to ascertain the attenuation of selected Endocrine Disruption Compounds (EDCs) from freely draining unsaturated subsoils receiving septic tank effluent and secondary treated effluent. The performance of secondary treatment and tertiary treatment horizontal subsurface flow reed beds was also studied with respect to EDC removal. The study showed that the development of a biomat across the percolation areas receiving secondary treated effluent was muted compared to the site receiving septic tank effluent on which the percolating effluent spread naturally by gravity over a much larger area. In general, the results showed the oestrogens (oestrone, oestrdiaol, ethynyloestradiol, and oestriol) percolating though the unsaturated subsoil were significantly degraded with depth down to very low values (<1 ng/L), with the exception of oestriol in the secondary treated effluent plume which seemed to be more persistent. There appeared to be little or no degradation of oestrogens under the saturated anaerobic conditions in the reed beds. The organic oxygen compound, bisphenol A, was not significantly reduced in the aerobic secondary treatment processes although some degradation was evident with depth through the subsoil in all trenches. Bisphenol A also showed no significant degradation in the reed bed environment. Finally, the study investigated the fate of caffeine (as a potential indicator of on-site effluent) which showed considerable removal in the aerobic subsoil conditions beneath all the trenches compared to little degradation of caffeine in the saturated anaerobic environment of the reed beds.

Wastewater treatment performance and sludge reduction properties of a household wastewater treatment system combined with an aerobic sludge digestion unit

On-site domestic wastewater treatment systems (Johkasous) have become popular in Japan and play an important role in controlling pollution of aquatic environments. Appropriate control of accumulated sludge is an important aspect of the use of these systems. With the goals of reducing sludge production and the total volume of the system, we developed and evaluated an experimental system. The total volume of the experimental (type I) system, which combined an aerobic sludge digester (ASD) with a wastewater treatment process, was 30% smaller than a conventional (type II) system. Both systems received the same domestic wastewater at a flow rate of 1.0 m 3 day −1 and were operated for 1 year. The sludge reduction ratio for the ASD of the type I system was 76.0%. The sludge produced in the type I system during the 1-year test was 12.62 kg, and the sludge yield based on removed biological oxygen demand (BOD) was evaluated to be 0.181 kg SS (kg BOD) −1. These values were approximately 35% less than those of the type II system (19.73 kg and 0.277 kg SS (kg BOD) −1, respectively). Although BOD and suspended solids (SS) in the final effluent were slightly higher than those from the type II system, the system we proposed may enable downsizing of the system volume and easier management of excess sludge.

A Comparison of Gravity Distribution Devices Used in On-Site Domestic Wastewater Treatment Systems

A detailed analysis of different types of gravity distribution devices, designed to split on-site wastewater effluent equally between percolation trenches, has been carried out both in the laboratory and also in the field under realistic loading conditions. Four different types of distribution device have been compared: a V-notch distribution box, stilling chamber box and tee-splitters with and without baffles. The trials carried out in the laboratory with clean water showed that flow distribution for all devices was sensitive to both the off-level installation angles and variable flow rates, with the most stable performance achieved using the flow splitter with upstream baffle plates. In parallel to this, the on-site flow regime experienced at two sites was continuously monitored using a tipping bucket and data-logger over twelve month periods, finding that the most common flow rates at the distribution unit were in the range of 0.1–2.5 l min−1. The on-site performance of these devices receiving both septic tank and secondary treated effluent showed that significant solid deposition and biofilm development had severely affected the equal distribution between the trenches, hence highlighting the need for regular maintenance to ensure efficient performance over time after installation.

Use of real-time PCR to examine the relationship between ammonia oxidizing bacterial populations and nitrogen removal efficiency in a small decentralized treatment system ‘Johkasou’

The aim of this study was to examine the relationship between ammonia oxidizing bacterial populations and biological nitrogen removal in a small on-site domestic wastewater treatment system "Johkasou". The population dynamics of ammonia oxidizing bacteria (AOB) in six full-scale advanced Johkasous was surveyed using real-time PCR assay over a period of one year. These Johkasous were selected to compare the AOB populations in different treatment performance. When the effluent NH4-N concentration was higher than 2 mg L(-1), it was difficult to meet the effluent standard of advanced Johkasous (T-N 10 mg L(-1)). In contrast, the nitrogen removal efficiency was hardly affected by nitrite oxidation and denitrification in these systems. In other words, ammonia oxidation was a rate-limiting step. Furthermore, we focused on the relationship between NH4-N loading per AOB cell and nitrogen removal. Real time PCR monitoring results demonstrated that it is important to regulate NH4-N loading per AOB cell below 210 pg cell(-1) day(-1) to meet the effluent standard of advanced Johkasou. It is considered that NH4-N loading per AOB cell is a useful parameter for determining suitable nitrogen loading and small decentralized system design.

Evaluation of an Economical Alternative Onsite Domestic Wastewater Treatment System to Remove Soluble and Particulate Organic Oxygen Demand

Evaluation of an Economical Alternative Onsite Domestic Wastewater Treatment System to Remove Soluble and Particulate Organic Oxygen Demand

Development of Phosphorus Removal Process of On-site Domestic Wastewater Treatment Systems Using Dripping Method of Thick Iron Solution.

An advanced technique of dripping the thick iron solution was developed and applied to on-site domestic wastewater treatment systems. The thick iron solution was obtained by heating and melting FeCl3⋅6H2O crystals.By using the new technique, the T-P concentration of the treated water decreased to less than 1mg·l-1 when the thick iron solution was added at an Fe/P molar ratio of 1.75. The addition of thick iron solution did not affect the removal of BOD, COD, SS and T-N.The T-P concentration of the treated water increased when coagulated sludge containing ferric phosphate was in contact with the anaerobic sludge in the tank for along time. This problem could be solved by improving the process to prevent such contact. It was also shown that the addition of thick iron solution increased the volume of sludge by about 30%.

嫌気槽に鉄材を浸漬する簡易なリン除去

A simplified phosphorus removal method for the small-scale on-site domestic wastewater treatment systems, which have been used for disposal of domestic wastewater, was examined.This method consisted of submerging the iron media in an anaerobic chamber. Phosphorus could be effectively removed even at a low oxygen concentration in the anaerobic chamber.The phosphorus removing effect in the anaerobic environment was examined in different iron media. Iron cations were dissolved from steel wool more than from other media, because of the relatively large surface area.The phosphorus removal method was examined using a continuous experimental apparatus. To obtain 90% phosphorus removal, it was necessary to submerge the iron media of 6.6kg·m-3 or more, and to maintain phosphorus-iron surface area loading to be 0.05g·m-2·d-1 or less.The iron surface was covered gradually with reaction products and captured SS, and the weight of iron increased. After 2 months of submersion of iron media, dissolution of iron cations was hindered, and phosphorus removal decreased markedly. Therefore, periodic back-wash at least every 2 months was considered necessary.Phosphorus removal cost was calculated. This method was considered to be expensive about 30-160%. However, it is possible to reduce the cost further by periodic maintenance.

エネルギー・アナリシスによる水循環システムの評価

This paper appraised 4 models of water recycle systems in urban area such as wastewater reuse system and rain water usage from the point of view of energy consumption.Input-output analysis was used for the calculation of energy consumption. Not only the direct energy such as electric power and fuel but also the indirect energy used for production of equipments or parts in the water system were taken into consideration.The main results obtained were as follows.(1) The least energy consumption model was unrecycle model.(2) The largest energy consumption model was individual recycle model, but in low-densed areas below 90-150 households/km2 it was advantageous than unrecycle model.(3) The energy consumption of wastewater reuse system was mainly attributed to the distribution system and was about 15% more than that of water works.(4) Recharge of groundwater by infiltration of rain water was better than on-site rain water usage because FRP water tanks consumed a large amount of energy.(5) Works such as water treatment or water distribution consumed about 50% of the maintenance energy in unrecycle model and the rest was considered to be consumed in the business in the works.(6) From the aspects of the energy consumption, johkaso (on-site domestic wastewater treatment system) was advantageous than sewage works in areas below 196 households/km2.