Autotrophic Denitrification with Granulated Sulfur and Limestone During Intermittent Operation

article in a collection out of WoS and Scopus

English

The sulfur-driven autotrophic denitrification (SDAD) process is based on the reduction of sulfur compounds, which act as electron donors for nitrate reduction. This process is therefore suitable for treatment of wastewater with a low C/N ratio. The SDAD process can be employed as a tertiary treatment of tailwater in small, domestic or wetland treatment plants. Granulated zero-valent sulfur is typically used to fill SDAD columns due to its good availability and low cost. During the SDAD, hydrogen ions are released, which causes a decrease in pH and thus a reduction in the functionality of denitrifiers. The addition of limestone as a buffer solves this problem. Limestone also serves as a carrier and carbon source for the microorganisms. Due to the often-uneven inflow of water to small treatment plants, this study focused on the impact of intermittent operation on denitrification. Laboratory experiments were conducted using columns fed with nitrate-enriched river water. Two of the most commonly used filling ratios (S:CaCO3 = 1:2 and 1:4) were tested in two different modes. Firstly, the NO3-N load was increased at a stable daily dosing time of 12 hours (mode 1). Secondly, the NO3-N load was fixed and the dosing time was gradually shortened (mode 2). In addition, one column (1:2) was operated without interruption as a control (mode C). The temperature, pH, nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N) and bicarbonate (HCO3-) concentrations were measured. If a hydrogen sulfide odor was identified in the effluent, the sulfides were also analyzed. The specific daily nitrate-nitrogen load (BN – inlet mass flow of NO3-N related to mass of S0 (mg/(g·d)) and the daily denitrification rate (rD – kg/(m3·d) – mass of denitrified NO3-N related to filling volume) were calculated. The best results were achieved when the columns were operated in mode 1, with rD achieving 0.25 kg/(m3·d) – mode 1-1:2 and 0.16 kg/(m3·d) – mode 1-1:4, respectively, when BN was 0.61 mg/(g·d). The nitrate removal efficacy was >90% in both cases. At the same BN, a similar denitrification rate of 0.28 kg/(m3·d) was achieved in mode C. In mode 2, the gradual shortening of the dosing time resulted in a reduction in the denitrification rate to 0.22 kg/(m³·d) for mode 2-1:2 and 0.15 kg/(m³·d) for mode 2-1:4. This was accompanied by a decline in nitrate removal efficacy to approximately 70%. Furthermore, intermittent operation also resulted in the formation of sulfides in column 1:2, which must be avoided. The SDAD is an applicable method for small treatment plants with highly fluctuating flow, if the formation of sulfides can be limited by maintaining a concentration of NO3-N in the treated water at approximately 5 mg/L.

denitrification, sustainable wastewater treatment, granulated sulfur

HRICH, K.; MALÁ, J.

30. 8. 2024

Thessaly, Greece

978-618-5765-04-0

11th International Conference on "Energy, Sustainability, and Climate Crisis" ESCC 2024

69

74

198

http://escc.uth.gr/escc-series/escc-2024/