A concept for planning and management of on-site and centralised municipal wastewater treatment systems, a case study in Bangkok, Thailand. I: pollutant discharge indicators and pollutant removal efficiency functions.

The concept of pollution load indicators for planning and management of the mixture conditions of centralised and on-site wastewater treatment systems has not been discussed in detail so far. In this paper, pollutant discharge (load) indicators and pollutant removal efficiencies were quantitatively analysed to develop a part of a strategy for planning and management of municipal wastewater treatment systems (WWTSs) under the mixture conditions in Bangkok, Thailand, as a case study. Pollutant discharge indicators of on-site WWTSs were estimated based on the relevant literature. Three kinds of pollutant removal efficiency function at centralised wastewater treatment plants (CWWTPs) were empirically developed for biological oxygen demand, chemical oxygen demand, total nitrogen, total phosphorus, total coliforms and faecal coliforms based on the existing CWWTP management data. These results will be integrated into the scenario-based analysis in the second paper in the series. The results will be base datasets, and the concept and estimation methods can be applied for wastewater treatment planning and management in other areas.

A concept for planning and management of on-site and centralised municipal wastewater treatment systems, a case study in Bangkok, Thailand. II: scenario-based pollutant load analysis.

Scenario-based pollutant load analysis was conducted to develop a part of a concept for planning and management of wastewater treatment systems (WWTSs) under the mixture conditions of centralised and on-site WWTSs. Pollutant discharge indicators and pollutant removal efficiency functions were applied from another paper in the series, which were developed based on the existing conditions in urban and peri-urban areas of Bangkok, Thailand. Two scenarios were developed to describe development directions of the mixture conditions. Scenario 1 involves keeping the on-site wastewater treatment plants (WWTPs) within the areas of centralised WWTSs. Scenario 2 is dividing the centralised and on-site WWTS areas. Comparison of the smallest values of total pollutant discharge per capita (PDCtotal) between Scenarios 1 and 2 showed that the smallest PDCtotal in Scenario 1 was smaller than that in Scenario 2 for biological oxygen demand, chemical oxygen demand and total phosphorus whereas the smallest PDCtotal in Scenario 2 was smaller than that in Scenario 1 for total nitrogen, total coliforms and faecal coliforms. The results suggest that the mixture conditions could be a possible reason for smaller pollutant concentrations at centralised WWTPs. Quantitative scenario-based estimation of PDCtotal is useful and a prerequisite in planning and management of WWTSs.

Linking sanitation and wastewater treatment: from evaluation on the basis of effluent pollutant concentrations to evaluation on the basis of pollutant removal efficiencies.

The evaluation of centralised wastewater treatment plants (WWTPs) in planning and management is sometimes based solely on effluent pollutant concentrations or pollutant loads. For sanitation purposes, the effluent pollutant concentrations/loads of WWTPs are important; of course, but from the point of view of wastewater treatment, the pollutant removal performance should also be evaluated. Focussing on low- and middle-income countries, especially those in tropical regions, published kinetics studies on biological WWTPs (such as oxidation ditches and aerated lagoons) are summarised in this paper. In most studies, effluent pollutant concentrations/loads are described as first-order linear functions of influent pollutant concentrations/loads. Therefore, pollutant removal efficiencies can be expressed as first-order linear functions of the reciprocal of influent pollutant concentrations/loads with negative coefficients. This implies that pollutant removal efficiencies increase with influent pollutant concentration/load increases. Based on pollutant removal efficiency functions, biological or ecological WWTPs when operating with small influent pollutant concentrations/loads should change their management to increase influent pollutant concentrations/loads in order to increase pollutant removal efficiencies. It may, however, be possible for technological development in wastewater treatment to overcome this problem.

Natural purification effects in the river in consideration with domestic wastewater pollutant discharge reduction effects.

The first social experiment program in Japan to reduce domestic wastewater pollutant discharge by "soft interventions" in households has been conducted in the Yamato-gawa River drainage area since 2005. The Yamato-gawa River has been listed as one of the worst water quality rivers in Japan because of the larger annual average BOD. "Hard interventions" including deployment of wastewater treatment facilities and artificial installation of natural purification facilities in the river has been conducted in these years to improve river water quality. At the first Yamato-gawa River social experiment program (YR-SEP) in March 2005, BOD at the monitoring point near the river mouth decreased about 6% during the Program. Natural purification effect along the river was evaluated in this article with one-dimensional water quality model for the six river sections. Larger biological oxygen consumption rate, kb, was estimated in the sections with artificially installed natural purification facilities. The effect of "soft interventions" in households in the YR-SEP was estimated as 25% BOD decrease in the nearest monitoring point to the river mouth, when all the households participate in the Program and BOD discharge reduction rate with "soft interventions" in households was 40%.

An index directly indicates land-based pollutant load contributions of domestic wastewater to the water pollution and its application.

As indices directly indicate land-based pollutant load contributions to public water pollution, pollutant load per capita flowing into the water body (PLCwb) for the drainage areas of inner city rivers in Chiba City, Chiba Prefecture, Japan, was analyzed. It was reaffirmed that PLCwb was different by the drainage area. For example, the biochemical oxygen demand (BOD) load per capita flowing into the water body (PLCwb-BOD) was calculated as 0.83 g BOD person(-1) day(-1) for population served with wastewater treatment plant (WWTP). In regards to the three types of on-site domestic wastewater treatment methods in Japan: 0.4-2.1 g BOD person(-1) day(-1) for combined jokaso (CJ), 4.5-21 g BOD person(-1) day(-1) for simple jokaso (SJ) and 4.3-19 g BOD person(-1) day(-1) for night soil treatment (NST). In regards to nutrient parameters of the three on-site treatment methods, population weighted average of PLCwb was [corrected] almost the same, however, relatively small PLCwb was [corrected] observed for CJ and SJ comparing to that for NST expecially in the drainage areas with smaller reaching ratios. [corrected] Environmental accounting housekeeping (EAH) books for domestic wastewater were prepared based on the analysis results as the application of the indices. EAH books are effective tools for water pollution mitigation in public water bodies. The results of the preliminary correlation analysis of the indices showed that high-efficiency treatment methods including WWTP, agriculture village wastewater treatment facility (AVETF) and CJ are effective in reducing pollutant load flowing into the water body, and that PLCwb have second-order equation relationships with population density of the drainage area. Judging from these characteristics and the analytical results of this study, PLCwb may be useful as an index for demonstrating the benefit of wastewater treatment in reduction of water pollution in the water body.