Sulfur Limestone 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.

Carbonate deposition and diagenesis in evaporitic environments: The evaporative and sulphur-bearing limestones during the settlement of the Messinian Salinity Crisis in Sicily and Calabria

Abstract The depositional and diagenetic processes involved in the formation of carbonates in the evaporitic environment of the Messinian Salinity Crisis are investigated in Southern Italy (Sicily and Calabria). Strong differences are observed between the studied sections that reflect specific depositional and diagenetic evolution in the interconnected sub-basins resulting from the syn-sedimentary tectonic fragmentation of the Central Sicilian and Calabrian domains. These carbonates formed diachronously in restricted perched sub-basins between the Tripoli Formation and the hypersaline settings of the MSC. The Calcare di Base (CdB) that can be interbedded with gypsum layers occurs rhythmically at the transition between the upper part of the Tripoli Formation and the massive gypsum, and at places synchronously with the deposition of the Lower Gypsum unit. It deposited initially as primary peloidal and microbial limestones, but their original structure and mineral composition were modified by the superimposition of early to late diagenetic processes. The first diagenetic step was the development of interstitially grown gypsum and halite crystals from trapped saturated brines that locally led to the formation of salt beds. The Sulphur Limestone (SL) resulted from the activity of sulphate reducing bacteria that occurred locally in the deeper parts of the various basins where anoxic bottom waters favoured microbial processes fuelled by biogenic methane and crude oil, and caused the carbonate replacement of gypsum and the formation of native sulphur. The migration of hydrocarbon and H 2 S-rich fluids caused the epigenetic dissemination of sulphur and a late diagenetic carbonate replacement of the gypsum. Later influxes of continental fresh waters were responsible for the dissolution of the halite crystals and their replacement by sparry calcite. The vugs, formed during both the gypsum/calcite conversion and the halite dissolution, either remained empty or were filled with calcite, celestine, fibrous silica, anhydrite, secondary gypsum, and native sulphur. The initial accumulation of fine-grained carbonate and gypsum sediments was strongly destabilised by volumetric changes resulting from mineral replacements and fluidisation processes. Their superimposition explains the vuggy and boxwork-like textures, in situ brecciation and lateral displacement, which are responsible for the chaotic organisation without necessarily involving basin-scale re-sedimentation in the form of debris flows.

Kinetics of autotrophic denitrification process and the impact of sulphur/limestone ratio on the process performance

Kinetics of sulphur–limestone autotrophic denitrification process in batch assays and the impact of sulphur/limestone ratio on the process performance in long-term operated packed-bed bioreactors were evaluated. The specific nitrate and nitrite reduction rates increased almost linearly with the increasing initial nitrate and nitrite concentrations, respectively. The process performance was evaluated in three parallel packed-bed bioreactors filled with different sulphur/limestone ratios (1:1, 2:1 and 3:1, v/v). Performances of the bioreactors were studied under varying nitrate loadings and hydraulic retention times (3–12 h). The maximum nitrate reduction rate of 0.66 g L−1 d−1 was observed at the loading rate of in the reactor with sulphur/limestone ratio of 3:1. Throughout the study, nitrite concentrations remained quite low (i.e. below 0.5 mg L−1 . The reactor performance increased in the order of sulphur/limestone ratio of 3:1, 2:1 and 1:1. Denaturing gradient gel electrophoresis analysis of 16S rRNA genes showed quite stable communities in the reactors with the presence of Methylo virgulaligni, Sulfurimonas autotrophica, Sulfurovum lithotrophicum, Thiobacillus aquaesulis and Sulfurimonas autotrophica related species.

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.

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.

Stable carbon isotopic composition of biogenic carbonates

The geology and sulfur isotopic composition of epigenetic pyrite of the Gas Hills district, Wyoming, indicate a bacterial origin for these sandstone-type uranium deposits. The δC 13 value of epigenetic calcite associated with organic materials, however, is heavier than the isotopic composition of calcite of biogenic native sulfur deposits. Stratigraphic and carbon isotopic evidence suggest that contamination by sedimentary carbonate is minimal in the Gas Hills samples. Field and laboratory data show that anaerobes produce isotopically heavier CO 2 and lighter methane than the associated organic material which they consume as an energy source. The δC 13 values of the salt-dome calcites overlap the methane field, the Gas Hills values overlap the CO 2 field, and analyses of Sicilian Sulfur limestones are intermediate. Deposits Gas Hills (calcites with organic material) Gulf Coast Cap rock Sicilian Sulfur limestone (gyngenetic calcites) Number of samples 20 35 27 Mean δC 13 −22.5 −37.9 −28.7 Sample standard deviation 4.0 6.7 8.9 Presumably a spectrum of values could be obtained by the oxidation of methane and contamination by the original bacterial CO 2 and sedimentary carbonate. The quantized values of the three deposits are, therefore, evidence of strong geologic control. Methane was stable under the reducing conditions (shown by the presence of uraninite and sulfides) of the Gas Hill, while methane was concentrated and oxidized in the cap rock of salt-domes (mineralogy includes native sulfur), and neither methane nor CO 2 was preferentially lost during the syngenetic precipitation of the Sicilian Sulfur limestone.

Geology and isotopic studies of Sicilian sulfur deposits

Stable isotopic studies of carbon and sulfur in correlation with geologic information have provided substantial evidence for a biogenic origin for native sulfur in salt domes. Similar studies on the Sicilian sulfur deposits indicate a biogenic syngenetic origin. Sulfur in Sicily occurs in a lagoonal evaporitic sequence of formations known as the Gypsum-Sulfur series of late Miocene age. The series, begins with the Diatomite formation that is overlain by the Basal limestone. Commercial quantities of sulfur occur in the next youngest formation known as the Sulfur limestone, the limestone of which is composed of white granular calcite. Alternating above the Sulfur limestone are the sulfurbarren Gypsum Beds formation and the Globigerina mail. The sigma S34 composition of the native sulfur in the sulfur limestone roughly varies between +l0 to --l0 permil, in contrast to differences between +20 to +30 permil for the sulfur in gypsum and anhydrite from which it is inferred the sulfur has been derived. These differences of a few permil to more than 20 permil are typical isotopic fractionations obtained during the reduction of sulfate to hydrogen sulfide by anaerobic bacteria. It is inferred that energy for the bacterial reduction was most likely provided by organic materialmore » that was oxidized by the bacteria to carbon dioxide which then reacted with calcium ions, made available by the reduced sulfate, to form calcite. This biological derivation of carbon dioxide, resulting in calcite in the Sulfur limestone, is suggested by sigma C/ sup 13/ variations between -20 to -30 permit for this formation, in contrast to typical sigma C/sup 13/ compositions of about -5 permil for carbonates in the other sulfur-barren formations. The almost complete lack of iron in the sediments that formed the sulfur limestone explains the lack of ferrous sulfide. Instead, it is inferred that the hydiogen sulfide was oxidized to native sulfur, in a suitable Eh environment having a limited supply of oxygen, by the expected exothermic reaction. It is, therefore, theorized that the Sicilian sedimentary sulfur deposits have a biogenic syngenetic origin. (auth)« less