Effects of Carrier Filling Ratio on Hydrogenotrophic Denitrification (HD) Performance

Abstract

The development of a low-cost and efficient hydrogenotrophic denitrification (HD) system for nitrate removal from groundwater is urgently required in developing countries. In the present study, a sponge-based HD reactor was developed to examine the effects of various carrier filling ratios (0%, 10%, 20%, and 30%) on the HD performance. HD reactors with sponges showed higher nitrogen removal capacities than that without sponges. There was no significant difference in the nitrogen removal efficiency at filling ratios of 10%, 20%, and 30%. The NO3-N removal rate varied based on the filling ratio, and reached 382, 470, 548, and 530 g-N/(m 3 ・ d) at filling ratios of 0%, 10%, 20%, and 30%, respectively. Furthermore, the attached biomass was considered to play an important role in the enhancement of NO3-N removal. The coexistence of hydrogenotrophic and heterotrophic denitrification activity was observed in the reactors, and there was a strong correlation between total volatile sponge-attached biomass and heterotrophic activity. However, heterotrophic activity accounted for a maximum of only 5.1% of the dissolved inorganic nitrogen removal. The high nitrogen removal rate achieved in this study shows that sponge-based HD reactors can potentially be used for NO3-N removal from groundwater.

Hydrogenotrophic Denitrification of Groundwater Using a Simplified Reactor for Drinking Water: A Case Study in the Kathmandu Valley, Nepal

“…However, the current economic situation and the energy affairs of the Kathmandu Valley could pose a challenge for the selection of water treatment technology, and the compatibility of these systems with the current social situation must be considered [8,9]. In this context, user-friendly water treatment systems that are low-cost, energy-efficient, compact, and easy to operate and maintain are desirable to ensure their sustainability [8,21]. From this perspective, physicochemical approaches, including ion exchange, reverse osmosis, and electrodialysis may be ineligible due to high capital infrastructure costs, high energy consumption, and the costs related to the disposal of waste brine [22].…”

“…Biological denitrification processes are broadly classified into two groups: heterotrophic and autotrophic denitrification, and the former has been conventionally studied for NO 3 − -N removal. The addition of organic carbon entailed in the activation of heterotrophic denitrification raises concerns regarding the increased risk of secondary pollution associated with elevated levels of total organic carbon [21,[23][24][25].…”

“…Recently, hydrogenotrophic denitrification (HD), which is a type of autotrophic denitrification, has drawn much attention as a promising technology for nitrate removal from groundwater [19,21,[23][24][25][26][27][28][29][30][31][32][33][34][35][36] because it offers certain advantages over heterotrophic denitrification systems. First, biomass generation can be reduced, thereby reducing clogging and the cost of post-treatment [33].…”

“…First, biomass generation can be reduced, thereby reducing clogging and the cost of post-treatment [33]. Second, there is no production of toxic waste as HD is a clean process [21,24]. Third, organic carbon is not necessary, leading to lower operational costs and lower risk of secondary contamination [23].…”

“…This leads to high costs for infrastructure and operation, frequent cleaning, post-treatment requirements, and high maintenance. In contrast, simplified HD systems, for example, using an attached growth reactor, can be well suited for application in developing countries owing to their user-friendliness [19,21,23]. To date, most research on the development of HD reactors for groundwater has been conducted in the laboratory using synthetic groundwater, and little information is available on the application of HD for raw groundwater treatment and the behavior of HD systems under on-site conditions.…”