Sulfur-limestone Autotrophic Denitrification Research Articles

Study on the removal of high nitrate-nitrogen concentration from pig farm wastewater by heterotrophic and sulphur autotrophic synergistic denitrification filter process

Following the anaerobic fermentation process in a lagoon, the effluent from pig wastewater exhibited elevated levels of total nitrogen and nitrate nitrogen. The utilization of simple sulphur-limestone autotrophic denitrification resulted in a sluggish reaction rate and relatively moderate removal load. To enhance the efficacy of the sulphur autotrophic denitrification process, a strategy was implemented involving the introduction of a limited quantity of corncobs as a slow-release carbon source. This addition was made to a sulphur-limestone autotrophic denitrification reactor that was being operated continuously and stably. Furthermore, the volume ratio of the corncobs added was progressively increased. This study examines the alterations in nitrate nitrogen, chemical oxygen demand (COD), sulphate, and alkali consumption within the sulphur-limestone autotrophic denitrification reactor, both prior to and after the introduction of corncobs. This study examines the operational efficiency and reaction mechanism of a sulfur-limestone autotrophic denitrification reactor that is enhanced by the utilization of corncobs as a slow-release carbon source. The findings of the study indicate that the inclusion of maize cob carbon source in the sulphur limestone autotrophic denitrification process resulted in improved effectiveness in removing nitrate and nitrogen. Additionally, when considering the three different ratios of corncob carbon source, the process exhibited a chemical oxygen demand (COD) removal rate exceeding 42%. The observed trend in the consumption of alkalinity in both the pure sulphur limestone autotrophic denitrification process and the sulphur limestone autotrophic denitrification process augmented by the three types of corncob slow-release carbon sources indicated an increase with time. The concentration of nitrate-nitrogen in the influent water exhibited a negative correlation with the length of the reactor flow-through. The addition of a slow-release carbon source derived from corncob greatly enhanced the autotrophic denitrification and denitrification impact in the three reactors. Moreover, there was an observed increase in the trend of heterotrophic denitrification as the amount of carbon source added increased. The efficacy of the mixotrophic denitrification process surpassed that of the sulphur-limestone autotrophic denitrification method in the treatment of nitrate-nitrogen wastewater characterized by a high concentration of nitrate-nitrogen. The former exhibited a higher denitrification rate and resulted in lower levels of sulphate ions and alkalinity production.

Mixotrophic denitrification: A study on the removal of high nitrate concentration from piggery wastewater by biofilter reactors

The treatment of piggery wastewater through anaerobic fermentation and subsequent irrigation on farmland has been found to pose a risk of nitrate-nitrogen pollution in groundwater, thereby posing potential threats to human health. The scientific investigation of employing heterotrophic/autotrophic (mixotrophic) denitrification as a means to address the issue of farm wastewater containing elevated levels of nitrate nitrogen has garnered significant attention. This study employed sulfur monomers, limestone, and corn cob as microbial carriers within a biofilter system to facilitate the heterotrophic denitrification process of piggery wastewater fermentation broth. The efficacy of mixotrophic denitrification was found to surpass that of sulfur-limestone autotrophic denitrification in the treatment of nitrate-nitrogen wastewater with elevated concentrations of nitrate-nitrogen. This was evidenced by higher rates of denitrification, as well as reduced production of sulphate ions and alkalinity. The experiments on mixotrophic denitrification reaction observed a positive correlation between the content of corn cob and the relative abundance of microbial flora. Specifically, the relative abundance of Proteobacteria at the phylum level showed an increasing trend. Additionally, there was a proportional increase in the relative abundance of various other flora at the genus level.

Pilot-scale application of sulfur-limestone autotrophic denitrification biofilter for municipal tailwater treatment: Performance and microbial community structure

This work aimed to study a pilot-scale sulfur-limestone autotrophic denitrification biofilter (SLADB) to remove nitrogen from municipal tailwater. The capacity of nitrogen removal and spatial distribution of microbial community at low temperature condition were analyzed. Low temperature inhibits nitrogen removal; while prolonging hydraulic retention time (HRT) increased nitrogen removal efficiency. TN and NO3−-N removal efficiency reached 81.1% and 85.3%, respectively, with HRT of 18 h at the temperature ranging from 6.4 to 9.8 °C. Proteobacteria and Chloroflexi were two dominant phyla. Along the reactor, class β-proteobacteria and ε-proteobacteria decreased, while γ-proteobacteria and Acidobacteria increased. For genus classification, Thiobacillus, Sulfurimonas, and Ferritrophicum which promote sulfur autotrophic denitrification, decreased significantly. While Anaerolineae promoting heterotrophic denitrification increased obviously. Sphingobacteriia coexisted in SLADB and were beneficial to nitrogen removal. Microbial community spatial distribution patterns were related to nitrogen removal. This study achieved reliable pilot-scale application of SLADB under low temperature for municipal tailwater.

Phosphorus removal in a sulfur–limestone autotrophic denitrification (SLAD) biofilter

The sulfur-limestone autotrophic denitrification (SLAD) biofilter was able to remove phosphorous from wastewater during autotrophic denitrification. Parameters influencing autotrophic denitrification in the SLAD biofilter, such as hydraulic retention time (HRT), influent nitrate (NO3(-)), and influent PO4(3-) concentrations, had significant effects on P removal. P removal was well correlated with total oxidized nitrogen (TON) removed in the SLAD biofilter; the more TON removed, the more efficient P removal was achieved. When treating the synthetic wastewater containing NO3(-)-N of 30 mg L(-1) and PO4(3-)-P of 15 mg L(-1), the SLAD biofilter removed phosphorus of 45% when the HRT was 6 h, in addition with TN removal of nearly 100%. The optimal phosphorus removal in the SLAD biofilter was around 60%. For the synthetic wastewater containing a PO4(3-)-P concentration of 15 mg L(-1), the main mechanism of phosphorus removal was the formation of calcium phosphate precipitates.

Nitrification and denitrification using biofilters packed with sulfur and limestone at a pilot-scale municipal wastewater treatment plant

A pilot-scale municipal wastewater treatment plant composed of a fixed film activated sludge (IFAS) system with sulfur–limestone autotrophic denitrification (SLAD) was operated for a year and the influence of different operational factors was investigated. Nitrification efficiency was found to be above 91% at temperatures above 25°C even at short hydraulic residence times (HRTs), but declined to 51±2% when the temperature dropped to 22±3°C. The minimum HRT (HRTmin) to achieve nitrification efficiency>90% was found to be 12 h at temperatures above 25°C. Denitrification efficiencies were found to be 89% and 79% at a nitrate loading of 0.36 kg NO-N m−3 d−1 and at 0.18 kg NO-N m−3 d−1, respectively. The minimum empty bed residence time (EBRT) to achieve denitrification efficiency above 80% without methanol addition was 3 h at a nitrate loading rate of 0.27–0.38 kg NO-N m−3 d−1. The amount of nitrate removed as a function of the sulfate formed was found to be 0.188 g NO-N/g SO. The nitrate load removed by the biofilter as a function of the alkalinity consumed was found to be very close to the theoretical stoichiometric value. The application of the pilot plant was proven to be feasible and the performance of the SLAD system, especially with respect to the minimum EBRT to achieve denitrification efficiency above 80%, the maximum denitrification rate and performance at temperatures below 10°C. To achieve a nitrification efficiency above 90% in the IFAS system, temperature changes and the minimum HRT were found to be the most influential operational parameters.

Development of a Response Surface for Prediction of Nitrate Removal in Sulfur–Limestone Autotrophic Denitrification Fixed-Bed Reactors

Sulfur–limestone autotrophic denitrification (SLAD) processes are very efficient for treatment of ground or surface water contaminated with nitrate. However, detailed information is not available on the interaction among some major variables on the design and performance of the SLAD process. In this study, the response surface method was used by designing a rotatable central composite test scheme with 12 SLAD column tests. A polynomial linear regression model was set up to quantitatively describe the relationship of the effluent and influent nitrate–nitrogen concentration and hydraulic retention time (HRT) in the SLAD column reactors. This model may be used for estimating the effluent nitrate–nitrogen concentration when the influent nitrate–nitrogen concentration ranges between 20 and 110 mg∕L and the HRT ranges between 2 and 9 h . Based on our model and the requirement for nitrite control, we recommend that the HRT of the SLAD column reactor be kept ⩾6 h and the nitrate loading rate less than 200 g N O3−...

Evaluation of kinetic parameters of a sulfur–limestone autotrophic denitrification biofilm process

In this study, four kinetic parameters of autotrophic denitrifiers in fixed-bed sulfur–limestone autotrophic denitrification (SLAD) columns were evaluated. The curve-matching method was used by conducting 22 non-steady-state tests for estimation of half-velocity constant, K s and maximum specific substrate utilization rate, k. To estimate the bacteria yield coefficient, Y and the decay coefficient, k d, two short term batch tests (before and after the starvation of the autotrophic denitrifiers) were conducted using a fixed-bed SLAD column where the biofilm was fully penetrated by nitrate-N. It was found that K s =0.398 mg NO 3 −–N/l, k=0.15 d −1, k d=0.09–0.12 d −1, and Y=0.85–1.11 g VSS/g NO 3 −–N. Our results are consistent with those obtained from SLAD biofilm processes, but different from those obtained from suspended-growth systems with thiosulfate or sulfur powders as the S source. The method developed in this study might be useful for estimation of four Monod-type kinetic parameters in other biofilm processes. However, cautions must be given when the estimated parameters are used because the measurements of the biomass and the biofilm thickness could be further improved, and the assumption of sulfur being a non-limiting substrate needs to be proved.

Pilot-Scale Evaluation of Select Nitrate Removal Technologies

Due to the extensive application of artificial nitrogen-based fertilizers and animal manure on land, many water agencies face problems of increasing concentrations of nitrate in groundwater. The contamination of groundwater by nitrate may pose a significant public health problem. The threat of methemoglobinemia is well documented and reflected in the US drinking water standard of 10 mg/L as nitrate-nitrogen. Approximately 45% of Saskatchewan's population use groundwater for drinking purposes, out of which, approximately 23% (230,000) are rural residents. The water used is made available from over 48,000 privately owned wells in regions where there is an extensive application of chemical fertilizers. Biological denitrification, ion exchange, and reverse osmosis (RO) processes were selected for a field study. Field studies were conducted on these processes. The sulfur/limestone autotrophic denitrification (SLAD) process was selected to achieve biological removal of nitrate from groundwater. The feasibility of the system was evaluated under anaerobic conditions. An ion exchange study was conducted using Ionac A554 which is a strong anion exchange resin. In the case of groundwater containing low sulfate concentrations, A554 offered high nitrate removal. However, the disposal of regenerant brine can be a problem. A reverse osmosis unit with Filmtec membrane elements (FT30-Element Family) was used in the study on nitrate removal. The unit effluent average nitrate concentration was less than the maximum allowable concentration.

Combined bioelectrochemical and sulfur autotrophic denitrification for drinking water treatment

A combined bioelectrochemical and sulfur autotrophic denitrification process for drinking water treatment was put forward and investigated extensively in this paper. In this new process, the bioelectrochemical denitrification was carried out in the upper part of the reactor while sulfur denitrification in the lower part. The H + produced in Sulfur Part could be consumed by hydrogen denitrification in Bioelectrochemical Part. Therefore, the limestone for pH adjustment in Sulfur Part was not necessary in this combined process, which avoided the problem of hardness increase. The sulfate accumulation in this combined reactor was less than that of the sulfur limestone autotrophic denitrification system. The effluent from two parts was kept neutral at optimum operation conditions. When the influent nitrate was 30 mg-N/L, the reactor could be operated efficiently at the hydraulic retention time ranged from 1.9 to 5 h (corresponding minimum current was 16–3 mA), i.e. the effluent NO 3 −-N removal ranged from 90% to 100% without nitrite accumulation and the effluent sulfate concentration was lower than 170 mg/L. The maximum volume-loading rate of the reactor was 0.381 kg NO 3 −-N/(m 3 d). The biomass and scanning electron microscope micrographs of Sulfur Part were also analyzed.

Nitrate Removal in Sulfur: Limestone Pond Reactors

The feasibility of using sulfur:limestone autotrophic denitrification (SLAD) pond reactors to treat nitrate-contaminated water or wastewater after secondary treatment was investigated with four lab-scale continuously fed SLAD ponds. The start-up period, temperature effects, and effects of different feed solutions were evaluated. With an influent concentration of 30 mg NO3--N/L at an HRT of 30 days, the pond reactors had an overall nitrate removal efficiency of 85–100%. Effluent nitrite concentrations were <0.2 mg N/L in all tests. Aerobic conditions could result in a decrease of the SLAD pH of the pond by 2 to 3 units and a large increase in sulfate production (∼1600-1800 mg-SO42-/L). Under unmixed (anoxic) conditions, the pH and sulfate produced were maintained at approximately 5.5 to 5.6 and 400-600 mg-SO42-/L, respectively, in all the SLAD ponds. Temperature affected the pond reactors adversely. By assuming that a first-order reaction occurred in a SLAD pond reactor, the temperature-activity coefficient, θ was found to be 1.068. Treatment of nitrate-contaminated surface water and wastewater using SLAD pond systems is feasible only if (1) the chemical oxygen demand (COD)/nitrate–N (COD/N) ratio is low (<1.2 with an initial NO3- concentration of 30 mg-N/L), (2) sulfur:limestone granules are not covered by sediment, and (3) sulfur-utilizing but nondenitrifying bacteria (SUNDB) are greatly inhibited due to the lack of DO in the pond systems. The SLAD ponds are not feasible for the treatment of raw wastewater or surface water if they contain high concentrations of organic matters due to the possible inhibition of sulfur-based autotrophic denitrifiers by heterotrophs (including heterotrophic denitrifiers). In addition, a high sulfate and low DO concentration as well as a low pH in the SLAD effluent of the pond (even when the pond is operated in an unmixed mode) also will limit the application of SLAD pond processes.

Removal of Nitrate in the Waste Water from High Bed Cultivation of Strawberry Using Sulfur-Limestone Autotrophic Denitrification

Removal of Nitrate in the Waste Water from High Bed Cultivation of Strawberry Using Sulfur-Limestone Autotrophic Denitrification

Nitrate Removal with Sulfur-Limestone Autotrophic Denitrification Processes

Nitrate removal using sulfur and limestone autotrophic denitrification (SLAD) processes was evaluated with four laboratory-scale fixed-bed column reactors. The research objectives were (1) to determine the optimum design criteria of the fixed-bed SLAD columns; and (2) to evaluate the effects of biofouling on the SLAD column performance. A maximum denitrification rate of 384 g NO3--N/(m3⋅day) was achieved at a loading rate between 600 and 700 g NO3--N/(m3⋅day). The effluent nitrite concentration started to rise gradually once the loading rate was above 600 g NO3--N/(m3⋅day). A loading rate between 175 and 225 g NO3--N/(m3⋅day) achieved the maximum nitrate-N removal efficiency (∼95%). Biofouling was evaluated based on tracer studies, the measured biofilm thickness, and modeling. The porosities of the columns fluctuated with time, and the elongation of the filter media was observed. Biofouling caused short-circuiting and decreased nitrate removal efficiency. A SLAD column will require backwashing after 6 months of operation when the influent is synthetic ground water but will foul and require backwashing within 1–2 months when the influent is real ground water.

Sulfur:limestone autotrophic denitrification processes for treatment of nitrate-contaminated water: batch experiments

In this study, an innovative process of using sulfur:limestone autotrophic denitrification (SLAD) for treatment of nitrate-contaminated surface or wastewater was put forward. The feasibility of this SLAD process was evaluated using lab-scale batch reactors operated under both aerobic and anaerobic conditions. Autotrophic denitrification occurred in batch reactors spiked with sulfur:limestone (S:L) under either aerobic or anaerobic conditions at both high ( ca. 300–500 mg NO 3 −–N/l) and low ( ca. 30 mg NO 3 −–N/l) initial nitrate concentrations. Nitrate–nitrogen removal increased with the addition of granular sulfur and limestone, while the addition of a seed of autotrophic denitrifiers into the batch reactors accelerated nitrate removal. Limestone was necessary to control the pH within the reactors. The optimum sulfur:limestone ratio was 3:1 (v/v) and the extent and rate of nitrate removal depended on the alkalinity within SLAD batch reactors. Nitrate removal efficiency, sulfate production and biomass accumulation were usually higher under aerobic conditions than under anaerobic conditions. Bacterial counts signified that both autotrophic denitrificans and nondenitrifying bacteria such as Thiobacillus thiooxidans were involved in the process under aerobic conditions. The SLAD process may be a replacement for heterotrophic denitrification in pond systems such as constructed wetlands or stabilization ponds due to the fact that no organic carbon source is needed in the SLAD process and that autotrophic denitrificans exist widely in natural sediments or soil.

Sulfur-based autotrophic denitrification pond systems for in-situ remediation of nitrate-contaminated surface water

The feasibility of using the sulfur/limestone autotrophic denitrification (SLAD) process as an in-situ method for remediation of nitrate-contaminated surface water was investigated. Four bench-scale pond systems with working volumes of 21.4 litres each and hydraulic retention time (HRT) of 30 days were operated under either mixed conditions or unmixed conditions. Under mixed (aerobic) conditions, with the addition of alkalinity to raise pH, NO3−-N removal in the SLAD ponds were 85-100%, while the control reactor showed negative removal. Sulfate production under mixed conditions, due to the activities of non-denitrifying bacteria such as Thiobacillus thiooxidans, was between 1000-2500 mg/l SO42−, which makes the application of the SLAD ponds under aerobic conditions questionable. Under unmixed (anoxic) conditions, NO3−-N removal in the SLAD ponds decreased to 75-88%; sulfate production, however, also decreased by more than 50% due to the inhibition of the activity of non-denitrifying bacteria. Additional batch experiments indicated that sulfate production in the SLAD systems was acceptable under anoxic conditions. Therefore, the application of the SLAD ponds under unmixed (anoxic) conditions is feasible for in-situ remediation of nitrate-contaminated surface water.

Sulfur-based autotrophic denitrification pond systems for in-situ remediation of nitrate-contaminated surface water

The feasibility of using the sulfur/limestone autotrophic denitrification (SLAD) process as an in-situ method for remediation of nitrate-contaminated surface water was investigated. Four bench-scale pond systems with working volumes of 21.4 litres each and hydraulic retention time (HRT) of 30 days were operated under either mixed conditions or unmixed conditions. Under mixed (aerobic) conditions, with the addition of alkalinity to raise pH, NO3−-N removal in the SLAD ponds were 85–100%, while the control reactor showed negative removal. Sulfate production under mixed conditions, due to the activities of non-denitrifying bacteria such as Thiobacillus thiooxidans, was between 1000–2500 mg/l SO42−, which makes the application of the SLAD ponds under aerobic conditions questionable. Under unmixed (anoxic) conditions, NO3−-N removal in the SLAD ponds decreased to 75–88%; sulfate production, however, also decreased by more than 50% due to the inhibition of the activity of non-denitrifying bacteria. Additional batch experiments indicated that sulfate production in the SLAD systems was acceptable under anoxic conditions. Therefore, the application of the SLAD ponds under unmixed (anoxic) conditions is feasible for in-situ remediation of nitrate-contaminated surface water.