DEWATS at Central Horticulture Center – “When there is a will there is always a way”

A popular saying goes – “Necessity is the mother of all inventions”. The case of construction of Decentralized Wastewater Treatment System (DEWATS) at Central Horticulture Centre (CHC) has a similar flavor to it. Central Horticulture Centre (CHC) located in Kritipur sub-municipality of Kathmandu district falls under Ministry of Agriculture and houses huge area of farmland for horticulture and conduct research related to it.

This article tells a story on how the dearth on water led them to materialize the concept of DEWATS. The implementation of the project was supported by Stockholm Institute of Technology (SEI) and technically supported by Environment and Public Health Organization (ENPHO) and Bremen Overseas Research and Development Association (BORDA) / Consortium of DEWATS Dissemination society (CDD).

CHC is the central level horticulture research and training centre that provides hands on training to farmers nationwide on horticulture practices. Similarly it also provides research ground for many researches on horticulture issues. It provides an opportunity for hands-on demonstration and research on horticulture, farming technologies, composting, vermi composting and urine application. The 3 hectares of horticulture farm produces 30,000 saplings of different kind of fruiting plants. However, they were facing huge water scarcity problem to irrigate their farmland. Dr. Janardhan Khadka from CHC revealed that they had to struggle with options to irrigate their lands. Dr. Khadka shared they had two options in their hands – first one was to install a boring system to extract the groundwater; another was to utilize the waste water flowing in the drainage system that flows through their premise. To economize the process as budget is always a main constrain they thus went with the latter option. They had being irrigating the land with the wastewater since then, unaware of the hazardous quality of the wastewater. Also, they felt that they had difficulty in the production of quality sapling with this, so they had to compromise the quality of the saplings they were producing. When the concept of DEWATS for wastewater treatment and reuse was known to them they had no second thoughts in installing the system. In this regards, DEWATS has been materialized as treatment of wastewater to be used in the farmland in large scale at the Central Horticulture Centre.

The system that has been installed at the CHC comprises of two step treatments - Diversion chamber with bar screen for primary treatment; and settling tank connected to Anaerobic Baffled Reactor (ABR). Since the wastewater has been planned for reuse in irrigation after the treatment, the system has been designed to incorporate these two step treatment. The treatment system has been design to treat 15 cum of daily wastewater flow which has been bypassed from the main trunk sewer flowing through the area. The waste from the diversion chamber then flows into the settler followed by ABR with 6 chambers. The effluent of the ABR is then utilized for the irrigation purpose. The design of the system has been done considering the Biological Oxygen Demand (BOD) value for the raw water to be 410 mg/L and COD value has been taken to be 1386mg/L. The design has been optimized in such a way as to obtained effluent BOD to be 57.5 mg/L and COD to be 254.3 mg/L which is preferable quality for the irrigation purpose. The system has also proposed to have a sludge drying bed to treat and reuse the sludge generated from the ABR.