Two factories in Ayutthaya and Krabi provinces in Thailand were chosen to develop an evaluation model to estimate the co-benefits of Clean Development Mechanism (CDM) for water environment improvement from biogas recovering projects. The valuation framework included the analysis of spatial scales of water quality perception to examine how stakeholders at different institutional scales attach values to sites. A questionnaire survey was used to elicit willingness-to-pay (WTP) with closed-end double-bounded questions for one-step improvement in river water quality from status quo. Water quality perception showed 79% of respondents agreed to pay with WTP varied across respondent groups. At the provincial scale, households in Ayutthaya had a higher WTP with an average of 77.9 baht/household/month, whereas, households at the national scale had a higher WTP of 75.3 baht/household/month for Krabi. With the censored regression model from the general perspective of water quality services, the most important endogenous variables associated with the WTP were household income and household members. Nevertheless, at the national scale, education and attitude factors became more important because of acknowledged public benefits in terms of land use in the provinces. Hence, it is proposed that the importance of spatial scale in water quality perception be measured and compared separately for co-benefits assessment.

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Artificial water storage ponds in the rural area around Khulna and Bagerhat Districts in Bangladesh were surveyed and categorized into domestic use (denoted as D), wastewater storage use (W), agriculture use (A) and fisheries use (F) for the rural ponds and urban domestic use (U: divided into large (Ul) and small groups (Us)). The main survey was carried out during the wet season and a part of the surveyed ponds was also investigated during the dry season. The area and volume of the ponds were large in Ul and F. The transparency was low in the category F, W and U ponds and the SS, TOC were higher in the category F and U ponds than the others. On the other hand the T-N and T-P were higher in category W and U ponds than the others. The size of all the ponds was decreased and the pond water changed more turbid during the dry season caused by increase of particulate matter in the water. The principal component analysis showed that the first component indicating the progress of eutrophication was largely contributed. The water quality of in rural domestic ponds especially during the dry season should be improved.

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A novel sewer pipe with a double-deck structure was developed for in-sewer treatment. The upper deck is designed for the smooth transportation of wastewater, while the treatment is conducted by sponge media in the lower deck, which is intermittently exposed to wastewater and oxygen as with a trickling filter. The performance of the novel pipe was examined in the pilot-scale demonstration fed with domestic wastewater for 9 months. The indices of organic matter (BOD, COD, and SS) decreased for several hours of batch-mode recirculating tests. The removal rates ranged between 12 and 39 g-COD/(m•d) and were not significantly affected by temperature (18 - 29°C) and flow rate (6 - 15 m³/h). The estimated oxygen requirement was balanced with the intermittent oxygen supply, i.e., sum of reaeration with water flow and direct exposure without water flow. Furthermore, the performance of the novel pipe coupled with simple post-treatments was also examined. The coagulation was the most efficient: BOD was successfully decreased to below 20 mg/L by the in-sewer treatment for 3.5 h followed by the addition of 100 mg/L of polyaluminum chloride. The novel pipe, therefore, may be promising technology for both COD reduction (independent usage) and alternative secondary treatment (coupled with coagulation).

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