Alkalinity Supplementation Research Articles

Simultaneous heterotrophic and sulfur-oxidizing autotrophic denitrification process for drinking water treatment: Control of sulfate production

A long-term performance of a packed-bed bioreactor containing sulfur and limestone was evaluated for the denitrification of drinking water. Autotrophic denitrification rate was limited by the slow dissolution rate of sulfur and limestone. Dissolution of limestone for alkalinity supplementation increased hardness due to release of Ca 2+. Sulfate production is the main disadvantage of the sulfur autotrophic denitrification process. The effluent sulfate concentration was reduced to values below drinking water guidelines by stimulating the simultaneous heterotrophic and autotrophic denitrification with methanol supplementation. Complete removal of 75 mg/L NO 3–N with effluent sulfate concentration of around 225 mg/L was achieved when methanol was supplemented at methanol/NO 3–N ratio of 1.67 (mg/mg), which was much lower than the theoretical value of 2.47 for heterotrophic denitrification. Batch studies showed that sulfur-based autotrophic NO 2–N reduction rate was around three times lower than the reduction rate of NO 3–N, which led to NO 2–N accumulation at high loadings.

Reduction of Alkalinity Supplement to a Novel High-rate UASB Reactor by a Multi-Feed Mode

Reduction of Alkalinity Supplement to a Novel High-rate UASB Reactor by a Multi-Feed Mode

Effect of Organic Load on the Performance and Methane Production of an AnSBBR Treating Effluent from Biodiesel Production

Currently, there is an increasing demand for the production of biodiesel and, consequently, there will be an increasing need to treat wastewaters resulting from the production process of this biofuel. The main objective of this work was, therefore, to investigate the effect of applied volumetric organic load (AVOL) on the efficiency, stability, and methane production of an anaerobic sequencing batch biofilm reactor applied to the treatment of effluent from biodiesel production. As inert support, polyurethane foam cubes were used in the reactor and mixing was accomplished by recirculating the liquid phase. Increase in AVOL resulted in a drop in organic matter removal efficiency and increase in total volatile acids in the effluent. AVOLs of 1.5, 3.0, 4.5 and 6.0g CODL(-1)day(-1) resulted in removal efficiencies of 92%, 81%, 67%, and 50%, for effluent filtered samples, and 91%, 80%, 63%, and 47%, for non-filtered samples, respectively, whereas total volatile acids concentrations in the effluent amounted to 42, 145, 386 and 729mgHAcL(-1), respectively. Moreover, on increasing AVOL from 1.5 to 4.5g CODL(-1)day(-1) methane production increased from 29.5 to 55.5N mLCH(4) gCOD(-1). However, this production dropped to 36.0N mLCH(4) gCOD(-1) when AVOL was increased to 6.0g CODL(-1)day(-1), likely due to the higher concentration of volatile acids in the reactor. Despite the higher concentration of volatile acids at the highest AVOL, alkalinity supplementation to the influent, in the form of sodium bicarbonate, at a ratio of 0.5-1.3g NaHCO(3) g COD (fed) (-1) , was sufficient to maintain the pH near neutral and guarantee process stability during reactor operation.

Efeito do bicarbonato de sódio no tratamento de vinhaça em AnSBBR operado a 55 e 35ºC

Avaliou-se a influência do bicarbonato de sódio (NaHCO3) no desempenho do reator anaeróbio batelada sequencial com biomassa imobilizada tratando vinhaça a 55 e a 35ºC. O reator foi preenchido com espuma de poliuretano e agitado a 300 rpm. A adaptação a 55ºC estendeu-se por 50 dias, tendo o reator sido alimentado com vinhaça (DQO de 0,3 a 1,0 g/L). Para a operação a 35ºC, procedeu-se inicialmente ao enriquecimento da população metanogênica, durante 21 dias, com substrato à base de etanol (2,5 gDQO/L). Posteriormente, cargas orgânicas volumétricas (COV) de 0,85 a 5,70 gDQO/L.d foram aplicadas no reator a 55ºC, com suplementação de 1,2 a 0,4 gHCO3-/gDQO. A 35ºC, o reator foi submetido a COV de 2,85 a 36,0 gDQO/L.d com 0,4 a 0,2 gHCO3-/gDQO. A remoção de DQO variou de 43 a 78% a 55ºC e de 75 a 85% a 35ºC. A suplementação de alcalinidade mostrou-se essencial para a estabilidade do processo, sendo requerida em menor quantidade a 35ºC.

Methanogenesis under acidic pH conditions in a semi-continuous reactor system

Operating an anaerobic digester at low pH could offer several advantages over operation at neutral pH. Most wastewater streams targeted for anaerobic digestion are inherently acidic, requiring alkalinity supplementation (at added expense) to buffer the pH at neutral. Additionally, previously published work completed by the authors using batch systems suggested that lowering the system pH could increase methane production by as much as 30%. The goal of this research was to evaluate the feasibility of sustaining methanogenesis at low pH in a semi-continuous laboratory-scale fermentor. Significant methane production was achieved in a system ranging in pH from approximately 4.0–5.3. Results show that, if the consortium is allowed to sufficiently acclimate to acidic conditions, methanogenesis can be maintained under acidic pH conditions, resulting in overall chemical oxygen demand (COD) reduction and methane production comparable to that achieved in a neutral pH system.

Nutrient recovery from anaerobically digested organic wastes

Effluents (digestates) resulting from anaerobic digestion of wet organic wastes can berecycled as fertilizers. Separation of such digestates into a wet and a dry fraction is common.The solid fraction is often sold as a soil enhancement product while the liquid fraction isusually discarded as wastewater. A large portion of the digestate nutrients is dissolved as ionsin the liquid. The aim of this study is to establish an efficient way to convert this into a liquid"organic fertilizer". Enhancement of the nutrient concentration is necessary in order to makethe final product commercially acceptable. Direct evaporative concentration is not suitable asit would lead to a significant loss of ammonia due to the fact that most of the availablenitrogen in these digestates is present in the ammonium/ammonia form. Thus stabilizing theproduct by partial nitrification prior to evaporation is proposed based on a series ofexperiments conducted to evaluate the appropriateness of this approach.The ammonium-N concentration of the digestate used was 1.7 g/L. The nitrification does notappear to be inhibited by ammonia, nitrate or nitrite accumulation, except when pH > 7.5, asituation that can be avoided by regulating the feeding rate based on pH measurements.Significant nitrite accumulation was not observed either. Nitrification is however consistentlylimited by alkalinity so that only about 75% of the ammonia can be converted to nitratewithout alkalinity supplementation. The nitrification brings the pH down below 5.0 where theremaining ammonia is present as> 99% NH/. At this condition the nitrified digestate can beevaporated without a significant nitrogen loss and the product is recognized to be a highquality liquid fertilizer. It is suggested that the production of concentrated partially nitrifiedorganic fertilizers can become a sustainable way of nutrient recovery from anaerobicdigestates originating from municipal organic wastes.

Whey Treatment by AnSBBR with Circulation: Effects of Organic Loading, Shock Loads, and Alkalinity Supplementation

The main objective of this work was to investigate the effect of volumetric loading rate (VLR), shock load, and alkalinity supplementation on the efficiency and stability of an Anaerobic Sequencing Batch Biofilm Reactor (AnSBBR) containing polyurethane foam cubes. Mixing in the reactor, which was kept at 30 +/- 1 degrees C, occurred by recirculating the liquid phase. The reactor treated 2.5 l cheese whey in 8-h cycles, at concentrations of 1, 2, and 4 g COD l-1, which corresponded to VLRs of 3, 6, and 12 g COD l-1 day-1, respectively. Application of single-cycle shock loads of 6, 12, and 24 g COD l-1 day-1 did not impair reactor performance. In addition, for VLRs of 3, 6, and 12 g COD l-1 day-1, alkalinity supplementation to the influent, at the end of each assay, could be reduced to 75, 50, and 50%, respectively, in relation to supplementation at the beginning of the assay. During reactor operation a viscous polymer-like material was formed between the polyurethane foam cubes, which increased at higher VLR. Finally, addition of salts to the influent improved reactor efficiency.

Anaerobic whey treatment by a stirred sequencing batch reactor (ASBR): effects of organic loading and supplemented alkalinity

An assessment was made of cheese whey treatment in a mechanically stirred anaerobic sequencing batch reactor (ASBR) containing granular biomass. The effect of increasing organic load and decreasing influent alkalinity supplementation (as sodium bicarbonate) was analyzed. The reactor operated on 8-h cycles with influent COD concentrations of 500, 1000, 2000 and 4000 mg/L, corresponding to volumetric organic loads of 0.6 to 4.8 mgCOD/L.d. Organic COD removal efficiencies were always above 90% for filtered samples. These results were obtained with an optimized alkalinity supplementation of 50% (ratio between mass of NaHCO 3 added and mass of influent mgNaHCO 3/mgCOD) in the assays with 500 and 1000 mgCOD/L and of 25% in the assays with 2000 and 4000 mgCOD/L. Initial alkalinity supplementation was equal to the mass of influent COD (100%). The system showed formation of viscous polymer-like substances. These were probably of microbiological origin occurring mainly at influent CODs of 2000 and 4000 mg/L and caused some biomass flotation. This could, however be controlled to enable efficient and stable reactor operation.

Strategies for alkalinity and pH control for ozonated shrimp pond water

In order to derive the full benefits of ozonation technology for the destruction of toxic metabolites in shrimp grow-out ponds, strategies to supplement and control high alkalinity loss during ammonia oxidation in a model ozonation system were studied. Alkalinity loss and pH profiles were investigated in the ozonated model system containing artificial seawater and ammonia, and alkalinity compensation ability of supplements such as calcium carbonate-based limes, hydrated limes and sodium bicarbonate were evaluated. In some experiments, application of these supplements during ozonation were combined with other treatments like recarbonation (external CO2 supply). Results showed that calcium carbonate-based limes were not anymore effective for alkalinity supplementation when ozonation is applied to seawater containing ammonia. Although recarbonation improved the effectiveness of CaCO3 as an alkalinity supplement, application in large ozonated grow-out ponds were considered not practical. The effective alkalinity supplements for ozonated seawater containing ammonia were the more soluble materials, high purity sodium bicarbonate and hydrated lime applied at a proper dosage. Sodium bicarbonate and hydrated lime would be more appropriate alkalinity control strategies for in situ1Ozonation inside grow-out pond.1 ozonated shrimp grow-out ponds; however, for application of hydrated lime, the problem of overdosage should be taken into consideration.

Maintaining granulation in a denitrifying upflow sludge-blanket reactor treating groundwater with low hardness.

Maintenance of denitrifying granular sludge for treating soft groundwater (total hardness = 75 mg calcium carbonate/L) in an upflow sludge-blanket reactor was demonstrated with complete removal of applied nitrate (20 mg N/L) over extended operation and a hydraulic residence time of 34 minutes. A high pH of approximately 9.0 was shown to be important for generation of mineral precipitation needed for production of heavy granular sludge with good retention characteristics. As a method of increasing precipitation potential, pH adjustment was determined to be more economically favorable than calcium or alkalinity supplementation. In addition, temporary increases in substrate loading were shown to be effective for enhancing biomass levels in a manageable granular sludge. The significance of biomass in promoting mineral precipitation was discussed.

Operating feasibility of anaerobic whey treatment in a stirred sequencing batch reactor containing immobilized biomass

The scope of this work was to evaluate the operating feasibility of anaerobic whey treatment in a stirred sequencing batch reactor (ASBR) containing biomass immobilized on inert support. Assays were performed using 8-hour cycles and agitation rate of 200 rpm at 30 +/- 1 degrees C, for treating cheese whey containing 500 to 4,000 mgCOD/L, which corresponded to a volumetric organic load (VOL) of 0.81 to 5.7 gCOD/L x d. Stability and high organic matter removal of about 96% were achieved at effluent concentration below 160 mgCOD/L for non filtered samples. Operating stability of the reactor was shown to be strongly dependent on the alkalinity supplementing strategy during the assay, especially during the startup period, where NaHCO3 supplementation was approximately 20-30% of the chemical oxygen demand (mgNaHCO3/mgCOD). After startup, alkalinity supplementation could be reduced down to 10% maintaining efficiency and stability. Moreover, proper homogenization of the system through mechanical agitation was also shown to be indispensable, especially with increasing organic load.

High‐Sulfate, High‐Chemical Oxygen Demand Wastewater Treatment Using Aerated Methanogenic Fluidized Beds

Many industrial wastewaters have both high organic pollution and sulfate (SO42) concentrations. Although biological conversion of organics to methane may be an economical chemical oxygen demand (COD) removal option, significant inhibition of methane production results from reduction of SO42 to hydrogen sulfide (H2S), which is inhibitory to methanogenic microorganisms. Therefore, sulfatecontaining wastewater is often not amenable to conventional anaerobic treatment. Recently, limited aeration of recycle flow to hybrid and baffled reactors has been used to treat this wastewater and has been shown to reduce aqueous H2S concentrations by causing production of uninhibitory sulfur (S°) and thiosulfate (S2O32) as well as gas stripping volatile H2S. In this study, directly aerated methanogenic fluidized bed reactors (FBRs) achieved increased methane production compared tostrictly anaerobic FBRs treating high‐sulfate wastewater. Oxygen transfer satisfying up to 28% of the COD load resulted in maximum specific oxygen utilization rates of 0.20 mg oxygen/g volatile solids min, with significant, concomitant methane production. Under typically inhibitory SO42 loading, higher aeration caused increased effluent SO42, increased H2S mass in the offgas, and lower reactor H2S concentration. As a result, COD removal increased from 25% for a strictly anaerobic FBR to 87% for an aerated FBR. In addition, aerated systems required significantly less alkalinity supplementation to maintain a pH value of 7, ostensibly because of stripping of acidic carbon dioxide. The potential pH increase associated with aeration also shifts sulfide speciation to less toxic bisulfide. Direct, limited aeration of methanogenic FBRs is described as a method for increased COD removal when treating highCOD, high‐sulfate wastewater

Anaerobic treatment of high-strength cheese-whey wastewaters in laboratory and pilot UASB-reactors

Start-up of the laboratory (3 l) UASB-reactor treating raw high-strength (up to 77 g COD/l) cheese-whey wastewaters as well as the treatment efficiencies (TE) and the maximal admissible organic loading rates (OLR) have been investigated under mesophilic (35°C) and submesophilic (20–30°C) conditions. A stable operation of the reactor with the TE higher than 90% on the total COD has been demonstrated up to the OLR of 28.5 and 9.5 g COD/l·day for mesophilic and submesophilic regimes, respectively. A successful start-up of the pilot (10.74 m 3) non-thermostated UASB-reactor treating raw cheese-whey wastewaters at ambient temperatures (ca. 24°C) has been completed in 3 months. Further exploitation of the reactor at the design OLR of 6.5 g COD/l·day showed its good operational stability with the TE close to 95% on the basis of total COD. After a proper start-up, the UASB-reactors can cope with preacidificated cheese-whey wastewaters (pH of about 4) even at elevated OLR that eliminates the necessity of alkalinity supplementation.

Palm oil mill effluent treatment by anaerobic baffled reactors: recycle effects and biokinetic parameters

In this study, the effects of recycle on anaerobic baffled reactor performances in treating palm oil mill effluents were investigated and biokinetic parameters were also determined. Recycle-ratio effect studies were carried out at the average loading rate of 15.6 g COD/l/d with the recycle rate varied from 5 to 25 times of the fresh-feed rate. The study shows that in the current system, a recycle of more than 15 times is needed to maintain the system pH higher than 6.8 without alkalinity supplementation, and the imposition of recycle is an effective means to reduce alkalinity requirements. Moreover, the kinetic model for substrate utilization and methane production proposed by Bathakur et al. (1991) was able to show the domination of certain culture in anaerobic processes. The model was also found to predict the experimental data of the present study with good accuracy.

Palm oil mill effluent treatment by anaerobic baffled reactors: Recycle effects and biokinetic parameters

In this study, the effects of recycle on anaerobic baffled reactor performances in treating palm oil mill effluents were investigated and biokinetic parameters were also determined. Recycle-ratio effect studies were carried out at the average loading rate of 15.6 g COD/l/d with the recycle rate varied from 5 to 25 times of the fresh-feed rate. The study shows that in the current system, a recycle of more than 15 times is needed to maintain the system pH higher than 6.8 without alkalinity supplementation, and the imposition of recycle is an effective means to reduce alkalinity requirements. Moreover, the kinetic model for substrate utilization and methane production proposed by Bathakur et al. (1991) was able to show the domination of certain culture in anaerobic processes. The model was also found to predict the experimental data of the present study with good accuracy.