Development of an attached growth reactor for NH₄–N removal at a drinking water supply system in Kathmandu Valley, Nepal

Abstract

Higher concentrations of ammonium (NH(4)-N) and iron (Fe) than a standard for drinking are typical characteristics of groundwater in the study area. To remove NH(4)-N and Fe, the drinking water supply system in this study consists of a series of treatment units (i.e., aeration and sedimentation, filtration, and chlorination); however, NH(4)-N in treated water is higher than a standard for drinking (i.e., <1.5 mg NH(4)-N/L). The objective of this study, therefore, is to develop an attached growth system containing a fiber carrier for reducing NH(4)-N concentration within a safe level in the treated water. To avoid the need of air supply for nitrification, groundwater was continuously dripped through the reactor. It made the system simple operation and energy efficient. Effects of reactor design (reactor length and carrier area) were studied to achieve a high NH(4)-N removal efficiency. In accordance with raw groundwater characteristics in the area, effects of low inorganic carbon (IC) and phosphate (PO(4)-P) and high Fe on the removal efficiency were also investigated. The results showed a significant increase in NH(4)-N removal efficiency with reactor length and carrier area. A low IC and PO(4)-P had no effect on NH(4)-N removal, whereas a high Fe decreased the efficiency significantly. The first 550 days operation of a pilot-scale reactor installed in the drinking water supply system showed a gradual increase in the efficiency, reaching to 95-100%, and stability in the performance even with increased flow rate from 210 to 860 L/day. The high efficiency of the present work was indicated because only less than 1 mg of NH(4)-N/L was left over in the treated water.

Investigation of the effects of hydrogenotrophic denitrification and anammox on the improvement of the quality of the drinking water supply system

“…The absence of the denitrification process is because of the high oxygen levels in the water (∼6 mg/L). [12] Therefore, under low oxygen conditions (< 0.3 mg/L), the number of hydrogenotrophic denitrification microorganisms increased to rich amounts in the HD reactor.…”

“…[6] A purification system including a NH 4 -N removal unit has been set up to provide safe drinking water for the residents. [12] The NH 4 -N removal unit (labeled as the pilot-scale nitrification reactor in Fig. 1a) and its recent performance parameters are presented in Figures 1b-1c.…”

“…[12] However, the NO 3 -N concentration was increased step-wise (by 10 mg/L) from 20 to 40 mg/L. During the preparation of the water containing NO 3 -N, the dissolved oxygen (DO) in tap water (used as the water source for synthetic water preparation) was reduced to <0.3 mg/L by feeding H 2 gas for 1 h.…”

“…2. [11] The nitrification system has been implemented for cleaning water supplies in several locations; [3,12] however, high levels of NO 3 -N (above the limits prescribed by the WHO) were reported. [13] Thus, an additional unit is required to remove the NO 3 -N present in the effluent from both the nitrification and anammox processes.…”

The Status of Domestic Water Demand: Supply Deficit in the Kathmandu Valley, Nepal

“…For the treatment of physicochemical contamination, the simple-in-operation, low cost, and energy efficient ammonia and nitrate removal system developed by Khanitchaidecha et al [17] could be used at the household or community scale. For iron removal, aeration, sedimentation and filtration before denitrification could be applied, as suggested by Khanitchaidecha et al [23].…”