Alkalinity Consumption Research Articles

S0-dependent bio-reduction for antimonate detoxification from wastewater by an autotrophic bioreactor with internal recirculation.

Elemental sulfur (S0) autotrophic reduction is a promising approach for antimonate [Sb(V)] removal from water; however, it is hard to achieve effective removal of total antimony (TSb). This study established internal recirculation in an S0 autotrophic bioreactor (SABIR) to enhance TSb removal from Sb(V)-contaminated water. Complete Sb(V) reduction (10mg/L) with bare residual Sb(III) (< 0.26mg/L) was achieved at hydraulic retention time (HRT) = 8h. Shortening HRT adversely affected the removal efficiencies of Sb(V) and TSb; meanwhile, an increased reflux ratio was conducive to Sb(V) and TSb removal at the same HRT. Sulfur disproportionation occurred in the SABIR and was the primary source for SO42- generation and alkalinity consumption. The alkalinity consumption decreased with the shortening HRT and increased with an increased reflux ratio at the same HRT. The generated SO42- was significantly higher (50-100 times) than the theoretical value for Sb(V) reduction. Coefficient of variation (CV), first-order kinetic models, and osmolality analyses showed that internal recirculation did not significantly affect the stability of SABIR but contributed to enhancing TSb removal by increasing mass transfer and reflowing generated sulfide back to the SABIR. SEM-EDS, Raman spectroscopy, XRD and XPS analyses identified that the precipitates in the SABIR were Sb2S3 and Sb-S compounds. In addition, high-throughput sequencing analysis revealed the microbial community structure's temporal and spatial distribution in the SABIR. Dominant genera, including unclassified-Proteobacteria (18.72-38.99%), Thiomonas (0.94-4.87%) and Desulfitobacterium (1.18-2.75%) might be responsible for Sb(V) bio-reduction and removal. This study provides a strategy to remove Sb from water effectively and supports the theoretical basis for the practical application of the SABIR in Sb(V)-contaminated wastewater.

Different fates of the coexisting Sb(V) and nitrate in sulfur autotrophic bioreactor mediated by internal circulation: Performance and mechanism

The sulfur autotrophic bioreactor with internal circulation was established for the simultaneous and effective removal of antimonate (Sb(V)) and nitrate (NO3−) in water for the first time. At the hydraulic retention time (HRT) of 8 h and the recycle ratio (R) of 5, the removal efficiency of Sb(V) and TSb reached up to 98.14 % and 96.89 % with a concentration of 10 mg/L Sb(V) in the influent. Although the shortening of HRT and the increase of R inhibited the removal of Sb(V) and TSb, there was little effect on the NO3− removal (> 97.08 % with the influent of 20 mg-N/L). Meanwhile, the measured concentration of sulfate (SO42−) and alkalinity consumption in effluent were both greater than theoretical value, indicating the occurrence of S0 disproportionation in bioreactor. The shortened HRT and declined R reduced alkalinity consumption, which hindered S0 disproportionation. The precipitates were collected at end of bioreactor operation period, which was confirmed to be Sb2S3 by SEM-EDS, Raman, XRD and XPS analysis. High-throughput sequencing results indicated that Proteobacteria and Bacteroidetes were the dominant bacteria at phylum level for denitrification. Besides, Sulfuriferula, Thiovirga and Sulfuricurvum (at genus level) might be accountable for bio-reduction of NO3− and Sb(V), as well as S0 disproportionation.

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.

Dynamics of the surface carbonate system in oil fields with a high concentration of wells on the northwestern South China Sea shelf

Oil exploitation may pose adverse effects on marine ecosystems, but its impacts on surface carbonate dynamics remain unknown. In a carbonate system with low air-sea ∆pCO2, such as the South China Sea (SCS), human activities may affect the pCO2 distribution patterns and potentially alter CO2 sink or source at the surface. This study investigates the surface carbonate system in two oil fields, namely the Wenchang Oil Feld and Enping Oil Feld, located on the northwestern SCS (NWSCS) shelf. In Enping Oil Field, although there is a slight increase in surface pCO2 due to probable total alkalinity (TA) consumption from CaCO3 precipitation, strong biological production makes the plume water a strong CO2 sink. Similarly, the biological processes dominated the pCO2 variability in Wenchang Oil Feld, exhibiting high values in its central area. In NWSCS, the influence of shelf water was observed during both cruises. And the pCO2 drawdown caused by the decreased sea surface temperature (SST) and CO2 outgassing outweighed their increases via enhanced vertical mixing, leading to a pCO2 drawdown from September to October within this water mass. More importantly, there were no significant disparities observed in carbonate parameters at stations along transects with and without wells, and the observed parameter values in this study fell within the range reported previously on the nSCS shelf with similar controlling processes. Thus the impact of oil exploitation on carbonate dynamics is negligible, and the characteristics of the carbonate system in oil field are primarily governed by natural processes such as the mixing of plume water and basin water, CaCO3 precipitation and the changes in SST. The provided data establish a crucial baseline for detecting future alterations in carbonate chemistry within oil fields, and the rapid fluctuations in sea surface pCO2 highlight the need for higher spatiotemporal resolution observation.

A pilot-scale study of a novel system for simultaneous nitrogen and carbon removal: technological advancement of a structured bed reactor with intermittent aeration (SBRIA) in real domestic sewage treatment.

This study outlines the development of an effective pilot-scale simultaneous denitrification and nitrification (SDN) system using intermittent aeration for the removal of carbon and nitrogen from real domestic sewage. Given the limited research in this area, the main objective was to evaluate the overall performance of the SBRIA system on a pilot scale and show its benefits in domestic wastewater treatment. The structured bed reactor with intermittent aeration (SBRIA) notably achieved 57% efficiency in removing total nitrogen without requiring external carbon sources. It also demonstrated impressive removal rates of 56% for total chemical oxygen demand (CODT) and 82% for biochemical oxygen demand (BOD5), indicating its effectiveness in degrading organic matter. In addition, the SBRIA showed high pH control and managed the consumption of alkalinity without the need for an alkalizer, maintaining consistent mean values of 7.7 ± 0.8 for pH and 166.8 ± 79.8 mg·L-1 for alkalinity. The system also proved resilient against toxic shocks caused by significant variations in influent characteristics. This study offers valuable insights and compelling results into a cost-effective and efficient treatment approach using an innovative technology not previously applied at the pilot scale. Its potential to remediate polluted water is substantial.

Long-term performance and biofilms of the novel nano manganese dioxide coupling carbon source pre-loaded biological activated carbon filters for drinking water

In order to accelerate the start-up of biological activated carbon (BAC) filters and enhance ammonium (NH4+-N) removal performance, three substrates (sucrose and/or nano manganese dioxide (nMnO2)) pre-loaded BAC filters were set up to investigate the pollutants removals and microbiological characteristics for a long-term operation of 197 days. The average NH4+-N removal performance treated by the sucrose coupled with nMnO2 loaded BAC filter was the highest (71.18 %), which was 3.83 times of that by the control filter (18.58 %). 29 % of NH4+-N treated by the sucrose coupled with nMnO2 loaded BAC removed through the traditional nitrification and denitrification, or simultaneous nitrification and denitrification (SND) pathways according to the calculation of the alkalinity consumption (6.12 mmol/L). There was no leakage of carbon source and Mn, and no accumulation of nitrite from the substrates loaded BAC. The dominant bacteria in the sucrose coupled with nMnO2 loaded BAC were Dechloromona (accounting for 8.02% of the total bacterial) and Acidaminobacter (accounting for 15.16% of total bacterial) on the Day 180, which had the capacity of nitrification or denitrification. NH4+-N and micropollutants removals treated by the combined process of peracetic acid (PAA) pre-oxidation and substrates loaded BAC were significant due to the generation of assimilable organic carbon (AOC) (5.98 ± 1.93 μg-C/mL) by PAA (100 μM)/Fe2+ pre-oxidation and the higher biomass ((4.57 ± 3.07) × 107 cells/g DW BAC) in the sucrose coupled with nMnO2 loaded BAC filter. Therefore, nMnO2 coupling carbon source pre-loading strategy could not only enhance initial colonization, but also promote pollutants removals for long-term operation.

Nature based solutions applied to mature leachate treatment in the Latin American resource-poor environment

Some Latin American countries have implemented environmental policies which have enhanced a shift in domestic solid waste practices from open dumps to sanitary landfills, bringing about a serious challenge to the region in terms of leachate management both in the operation and the aftercare phases of landfills. This work looks at the viability of Nature based Solutions (NbS) in the Latin American resource-poor environment as a cost-efficient alternative for dealing with such a challenge. In particular, an experimental trial was carried out in order to evaluate the contaminants removal of four subsurface constructed wetlands at a pilot scale, for treating mature leachate with emphasis on nitrogen removal. The wetlands were set in two treatment lines: (1) a vertical flow wetland followed by a horizontal flow wetland and (2) two vertical flow wetlands in series. Each line was fed at a 173 L.d−1 rate of mature leachate. The wetlands were planted with a polyculture of the tropical plants Colocasia esculenta and Heliconia psittacorum in a random way and the support media used was composed of 3/8″ gravel and gross sand. Both treatment lines showed similar behaviours and it is important to highlight that ammoniacal nitrogen, that is the principal contaminant to treat, was significantly removed (40% approx.) considering the high loads the system was fed with (490 kg.d−1 TAN). It is considered that the removal mechanism of the ammoniacal nitrogen is a biological nitrification-denitrification process, due to the increase of nitrite and nitrate concentrations in the effluent, as well as the bicarbonate alkalinity consumption. These results suggest the system proposed as an NbS has promising potential for leachate treatment in Latin American countries.

Achieving nitrogen removal with low material and energy consumption through partial nitrification coupled with short-cut sulfur autotrophic denitrification in a single-stage SBR

An innovative partial nitrification and short-cut sulfur autotrophic denitrification (PN-SSAD, NH4+-N → NO2−-N → N2) coupled system in a single-stage SBR was proposed to treat low C/N wastewater with low material and energy consumption. Nearly 50 % alkalinity consumption and 40 % sulfate production were reduced in S0-SSAD compared with S0-SAD, whereas the autotrophic denitrification rate was increased by 65 %. In S0-PN-SSAD, the TN removal efficiency reached almost 99 % without additional organic carbon. Furthermore, pyrite (FeS2) rather than S0 served as the electron donor to optimize the PN-SSAD process. The practical sulfate production in S0-PN-SSAD and FeS2-PN-SSAD were about 38 % and 52 % lower than complete nitrification and sulfur autotrophic denitrification (CN-SAD), respectively. Thiobacillus was the major autotrophic denitrification bacteria in S0-PN-SSAD (34.47 %) and FeS2-PN-SSAD (14.88 %). Nitrosomonas and Thiobacillus played a synergistic effect in the coupled system. FeS2-PN-SSAD is expected as an alternative technology for nitrification and heterotrophic denitrification (HD) in treating low C/N wastewater.

Potential of anaerobic co-digestion of acidic fruit processing waste and waste-activated sludge for biogas production

Abstract The potential of acidic fruit processing waste (FPW) and waste-activated sludge (WAS) co-digestion for methane production was investigated using batch and continuous experiments. First, batch experiments showed the co-digestion of FPW and WAS solved acid accumulation and increased cumulative biogas production. When the volatile solid (VS) ratio of FPW to WAS was 2:1, the cumulative biogas production was the highest (4,695.47 mL), which increased by 5.2% and 10.5% compared with the VS ratios of 3:1 and 1:1, respectively. Methane production was the rate-limiting step when the FPW percentage was high, and hydrolysis was the rate-limiting step when the WAS percentage was high. Second, the continuous experiments showed fermentation was the most stable when the VS ratio was 2:1, without acid accumulation or excessive total alkalinity consumption. Additionally, the ammonia nitrogen content in the system was above 138.34 mg·L−1, which solved the slow WAS hydrolysis rate and low nitrogen supply efficiency. Microbial community structure of the reactor was correlated with substrate composition greatly. On the 180th day, the relative abundance levels of Bacteroides, Paludibacter, Litorilinea, Levilinea, and Smithella were higher than those on the 120th day and the 240th day. The enrichment of those bacterial groups was beneficial to improve the substrate hydrolysis rate and reduce the influence of organic acids on the anaerobic system.

Application of tannin-based coagulant for high-range turbidity surface water clarification

Abstract This study aimed to evaluate the performance of a tannin-based coagulant in clarifying drinking water from a high-range turbidity river and characterizing the sludge. Tanfloc MTH product was selected for this investigation. The study site was surface water located in southern Brazil (Caveiras River, Brazil). Samples were collected just before the Parshall flume in the municipal water treatment plant in Lages (Brazil) for nine months, at least once a week. Jar testing evaluated turbidity removal, alkalinity consumption, optimal coagulant dosage, and settling velocity. After flocculation and settling, the sludge generated from the jar test was submitted to metal and thermogravimetric analyses. The use of tannin reduced the average water turbidity from 26.1 ± 56.1 to 0.94 ± 0.26 NTU, apparent color from 145 ± 190 to 3 ± 3 Pt-Co, and there was no variation in the pH. Additionally, the settling velocity of the flocs reached a maximum turbidity removal at 3.5 cm·min−1. Furthermore, the metal concentrations in the sludge showed a majority of aluminum and iron, and thermogravimetric analysis revealed 64% weight loss. In conclusion, Tanfloc presented the potential to be used in surface water clarification from the Caveiras river, and the extensive turbidity range observed during this study did not affect the operational stability.

Construction of heterotrophic-sulfur autotrophic integrated fluidized bed reactor for simultaneous and efficient removal of compound pollution of perchlorate and nitrate in water

A heterotrophic sulfur autotrophic integrated fluidized bed reactor was established for simultaneous and efficient removal of ClO4− and NO3− from water. The optimum operating conditions forecasted through the response surface method (RSM) were the hydraulic retention time (HRT) of 0.50 h, the influent acetate (CH3COO−) concentration of 55 mg/L and the reflux ratio of 14, contributing to ClO4− and NO3− removal of 98.99% and 99.96%, respectively, without secondary pollution caused by residual carbon (NPOC <3.89 mg/L). Meanwhile, the effluent pH fluctuated in a range of 6.70–8.02 and sulfur-containing by-products (i.e., SO42− and S2−) could be controlled by adjusting operation conditions throughout the experimental stage. The increase of the influent CH3COO− concentration reduced the load borne by autotrophic reduction process and further reduced SO42− production. Shortening HRT, increasing the influent CH3COO− concentration and decreasing the reflux ratio could all reduce alkalinity consumption. Shortening HRT and decreasing the reflux ratio could shorten contact time between sulfur and water and thus inhibit S0 disproportionation. High-throughput sequencing result showed that Proteobacteria and Chlorobi were the dominant bacteria. Sulfurovum, Sulfuricurvum and Ignavibacterium were the major heterotrophic denitrifying bacteria (DB)/perchlorate reducing bacteria (PRB), Ferritrophicum and Geothrix were DB, and Chlorobaculum was S0 disproportionation bacteria.

Coupled sulfur and electrode-driven autotrophic denitrification for significantly enhanced nitrate removal

Elemental sulfur (S0)-based autotrophic denitrification (SAD) has gained intensive attention in the treatment of secondary effluent for its low cost, high efficiency, and good stability. However, in practice, the supplementary addition of limestone is necessary to balance the alkalinity consumption during SAD operation, which increases water hardness and reduces the effective reaction volume. In this study, a coupled sulfur and electrode-driven autotrophic denitrification (SEAD) process was proposed with superior nitrate removal performance, less accumulation of sulfate, and self-balance of acidity-alkalinity capacity by regulating the applied voltage. The dual-channel electron supply from S0 and electrodes made the nitrate removal rate constant k in the SEAD process 3.7-5.1 and 1.4-3.5 times higher than that of the single electrode- and sulfur-driven systems, respectively. The S° contributed to 75.3%-83.1% of nitrate removal and the sulfate yield during SEAD (5.67-6.26 mg SO42−/mg NO3−-N) was decreased by 17%-25% compared with SAD. The S0 particle and electrode both as active bio-carriers constructed collaborative denitrification communities and functional genes. Pseudomonas, Ralstonia and Brevundimonas were the dominant denitrifying genera in S0 particle biofilm, while Pseudomonas, Chryseobacterium, Pantoea and Comamonas became dominant denitrifying genera in the cathode biofilm. The narG/Z/H/Y/I/V, nxrA/B, napA/B, nirS/K, norB/C and nosZ were potential functional genes for efficient nitrate reduction during the SEAD process. Metagenomic sequencing indicated that S0 as an electron donor has greater potential for complete denitrification than the electrode. These findings revealed the potential of SEAD for acting as a highly efficient post denitrification process.

Coupling of endogenous/exogenous nitrification and denitrification in an aerobic granular sequencing batch reactor

ABSTRACT The performance of endogenous/exogenous nitrification and denitrification in an aerobic granular sequencing batch reactor was investigated for treating inorganic wastewater with ammonia nitrogen of 250 mg/L. The sequencing batch reactor with an effective volume of 120.5 L was started by seeding autotrophic nitrifying granular sludge (ANGS) and operated under oxic (110 min)/anoxic (120 min)/oxic (110 min) aeration mode. The total inorganic nitrogen (TIN) removal efficiency of ANGS was between 60% and 70% without external carbon sources in days 1–25. However, the operation mode was unsustainable as endogenous nitrification and denitrification would lead to an obvious decrease of sludge concentration. After sodium acetate (the contributed chemical oxygen demand in the reactor was 250–300 mg/L) was added at the beginning of the anaerobic/anoxic stage from day 26, aerobic granules were inadaptable in a few days, which resulted in particle disintegration and SVI increase. As microbes gradually acclimated to the new environment, the aerobic granular sludge became smoother and denser, the relative abundance of denitrifying bacteria increased to 66.07%, and the removal efficiency of TIN gradually increased to more than 90% from day 89. Contributions of endogenous/exogenous nitrification and denitrification to TIN removal were 54.09% and 46.01%, respectively. The coupling of endogenous/exogenous nitrification and denitrification could reduce the aeration consumption, save the external carbon source dosage and decrease the alkalinity consumption, which provided another option for treating wastewater from ionic rare earth mine.

New insight into scale inhibition during tea brewing: Ca2+/Mg2+ complexing and alkalinity consumption

Scale not only affects the taste and color of water, but also increases the risks of osteoporosis and cardiovascular diseases associated with drinking it. As a popular beverage, tea is rich many substances that have considerable potential for scale inhibition, including protein, tea polyphenols and organic acids. In this study, the effect of tea brewing on scale formation was explored. It was found that the proteins, catechins and organic acids in tea leaves could be released when the green tea was brewed in water with sufficient hardness and alkalinity. The tea-released protein was able to provide carboxyl groups to chelate with calcium ions (Ca2+), preventing the Ca2+ from reacting with the carbonate ions (CO32−). The B rings of catechins were another important structure in the complexation of Ca2+ and magnesium ions (Mg2+). The carboxyl and hydroxyl groups on the organic acids was able to form five-membered chelating rings with Ca2+ and Mg2+, resulting in a significant decrease in Ca2+ from 100.0 to 60.0 mg/L. Additionally, the hydrogen ions (H+) provided by the organic acids consumed and decreased the alkalinity of the water from 250.0 to 131.4 mg/L, leading to a remarkable reduction in pH from 8.93 to 7.73. It further prevented the bicarbonate (HCO3−) from producing CO32− when the water was heated. The reaction of the tea constituents with the hardness and alkalinity inhibited the formation of scale, leading to a significant decrease in turbidity from 10.6 to 1.4 NTU. Overall, this study provides information to help build towards an understanding of the scale inhibition properties of tea and the prospects of tea for anti-scaling in industrial applications.

The influence of alkalinity on the two stages of S0-based autotrophic denitrification

In this study, two S0 particle packed reactors were constructed to explore the influence of alkalinity content on S0-based autotrophic denitrification (SAD) with nitrate and nitrite as electron acceptors respectively. As a result of the comparative experiment, when the alkalinity of influent is sufficient (HCO3 -: NO3 - mole ratio > 1.5:1), NO3 --N and NO2 --N reactor both showed high removal efficiency. But when the HCO3 -: NO3 - mole ratio decreased to 0.2:1, the average removal rate of NO3 --N decreased to 31%, and NO2 --N average removal rate still maintained at 95%. Based on the results, the reduction of alkalinity can significantly reduce the nitrate removal efficiency, but has little effect on the nitrite removal efficiency. This study further explained the characteristics of alkalinity consumption of the two stage of SAD and may provide a reference for future research.

Two Decades of Experience with the Granular Sludge-Based ANAMMOX® Process Treating Municipal and Industrial Effluents

This paper is a review of 20 years of full-scale experience with the granular sludge-based ANAMMOX process. The ANAMMOX process is a biological deammonification process for energy-efficient removal of ammoniacal nitrogen, which has been successfully applied on dewatering reject liquors from biosolids sludge digesters (e.g., mesophilic anaerobic digestions, codigestion, thermal sludge hydrolysis process (THP)) and nutrient-rich anaerobically treated industrial effluents (e.g., fermentation industry, food industry). The ANAMMOX process is a continuously operated biological process using granular biomass. The highly active concentrated granular biomass allows for compact reactor systems and a fast start-up. Long term operations of various case studies show stable process performance of full-scale reactors treating municipal and industrial effluents, achieving ammoniacal nitrogen (NH4-N) removal in excess of 90% at low and high loading rates up to 2.5 kgNH4-N/(m3·d). Some special aspects (e.g., micro-nutrients, inhibition, alkalinity consumption) of treating various wastewaters are discussed in detail. The ANAMMOX process is demonstrated to be resilient in handling process upsets and off-spec wastewater composition.

Efficient Nitrification and Low-Level N2O Emission in a Weakly Acidic Bioreactor at Low Dissolved-Oxygen Levels Are Due to Comammox.

Nitrification is an essential process for nutrient removal from wastewater and an important emission source of nitrous oxide (N2O), which is a powerful greenhouse gas and a dominant ozone-depleting substance. In this study, nitrification and N2O emissions were tested in two weakly acidic (pH 6.3 to 6.8) reactors: one with dissolved oxygen (DO) at over 2.0 mg/liter and the other with DO at approximately 0.5 mg/liter. Efficient nitrification was achieved in both reactors. Compared to that in the high-DO reactor, N2O emission in the low-DO reactor decreased slightly, by 20%, and had insignificant correlation with the fluctuations of DO (P = 0.935) and nitrite (P = 0.713), indicating that N2O might not be produced mainly via nitrifier denitrification. Based on quantitative PCR (qPCR), quantitative fluorescent in situ hybridization (qFISH), and functional gene amplicon and metagenome sequencing, it was found that complete ammonia oxidizers (comammox), i.e., Nitrospira organisms, significantly outnumbered canonical ammonia-oxidizing bacteria (AOB) in both weakly acidic reactors, especially in the low-DO reactor with the comammox/AOB amoA gene ratio increasing from 6.6 to 17.1. Therefore, it was speculated that the enriched comammox was the primary cause for the slightly decreased N2O emission under long-term low DO in the weakly acidic reactor. This study demonstrated that the comammox Nitrospira can survive well under the weakly acidic and low-DO conditions, implying that achieving efficient nitrification with low N2O emission as well as low energy and alkalinity consumption is feasible for wastewater treatment.IMPORTANCE Nitrification in wastewater treatment is an important process for eutrophication control and an emission source for the greenhouse gas N2O. The nitrifying process is usually operated at a slightly alkaline pH and high DO (>2 mg/liter) to ensure efficient nitrification. However, it consumes a large amount of energy and chemicals, especially for wastewater without sufficient alkalinity. This paper demonstrates that comammox can adapt well to the weakly acidic and low-DO bioreactors, with a result of efficient nitrification and low N2O emission. These findings indicate that comammox organisms are significant for sustainable wastewater treatment, which provides an opportunity to achieve efficient nitrification with low N2O production as well as low energy and chemical consumption simultaneously.

Use of Moringa oleifera seed as a natural coagulant in domestic wastewater tertiary treatment: Physicochemical, cytotoxicity and bacterial load evaluation

This study aimed to evaluate the use of Moringa oleifera (MO) seed aqueous extract for tertiary treatment of a domestic wastewater by coagulation, flocculation, sedimentation, and rapid granular filtration. Jar tests with sand filter coupled were performed in secondary effluent samples with MO and alum dosages to evaluate the capacity to remove apparent color, turbidity, BOD, COD, TOC, nutrients, generated sludge, pH, and alkalinity consumption. Effects on the bacterial load (total coliforms and Escherichia coli), antibacterial activity in vitro (Escherichia coli Strain ATCC 25922), and cytotoxicity (Vero cells) were also evaluated. MO at the optimal dosage of 600 mg/L showed results statistically equal to the use of alum (200 mg/L), achieving bacterial load, turbidity, and apparent color removal higher than 99 %, 92 %, and 66 %, respectively. Differently from alum, the MO dosage increase did not consume alkalinity or change pH value. MO produced a more organic sludge, with total solids 1.8 times lower, and 3 times less bulky sludge than alum. Treatment with MO did not remove nutrients and increased organic matter (BOD, COD, and TOC). However, treatment with MO resulted in an effluent with less cytotoxicity, when compared with alum. MO did not show significant antibacterial activity, which may be related to the applied dosages. These results emphasized that MO seed aqueous extract has the potential to be used as a coagulant for domestic wastewater tertiary treatment, but a purification process of extracting cationic proteins from MO seeds is recommended when the effluent organic load is a concern.

Identifying the best coagulant for simultaneous water treatment objectives: Interactions of mononuclear and polynuclear aluminum species with different natural organic matter fractions

As some water utilities are facing increasing concentrations of natural organic matter (NOM) in source water, it has been observed that some of this organic content is refractory to conventional coagulation treatment with alum and ferric sulfate. However, prehydrolyzed coagulants containing polymeric and/or cationic aluminum species such as Al2, Al3, Al13, and Al30 offer many advantages over conventional metal salts, including improved removal of hydrophilic compounds, stronger electrostatic interactions with anionic functional groups, better stability over a wider pH range, etc. Residual NOM after coagulation was characterized using liquid chromatography–organic carbon detection–organic nitrogen detection (LC-OCD-OND), while aluminum species were identified using nuclear magnetic resonance (NMR). Six coagulants having different proportion of Al species were tested on three surface waters, and guidelines for the coagulant selection are proposed for different NOM fractions: humics (HS), building blocks (BB, breakdown products of HS), low molecular weight acids (LMWa), low molecular weight neutral (LMWn) compounds, biopolymers (BP), and dissolved organic nitrogen from the HS fraction (HS-DON). In summary, ferric sulfate outperformed aluminum-based coagulants in acidic conditions (pH < 6) while aluminum chlorohydrate (basicity of 83 %) was repeatedly noted to be the best coagulant in more alkaline conditions (pH > 7). Under more neutral pH (6–7), alum offered a good compromise between DOC and turbidity removals and the coagulant cost. Coagulant performance was also assessed based on typical indicators used in the industry such as turbidity, dissolved organic carbon (DOC), residual aluminum/iron, trihalomethanes/haloacetic acids (THM/HAA) precursors, and alkalinity consumption. Considering all indicators and NOM fractions, this study revealed that PAX 14, a slightly prehydrolyzed coagulant (basicity of 23 %), exhibited the best performance during enhanced coagulation at pH 6.0.

Research into application of polyaluminum chlorides in coagulation of pollutants in reservoir waters with a wide range of pH

Reservoir waters extracted during exploitation of crude oil and natural gas are a serious threat to the environment. The reason is high content of dissolved salts, mainly chlorides, as well as toxic components, such as: petroleum substances with aromatic hydrocarbons, and various chemicals applied during hydrocarbons production, e.g. corrosion, hydrates and paraffin inhibitors, surfactants, methanol etc. For this reason, the extracted reservoir water should be managed in a way that is least harmful to the environment. One of the methods of management that meets this requirement is injection of reservoir water into the absorptive horizon. In order to provide failure-free injection, with maximum use of the capabilities of an absorptive horizon, it is necessary to prepare the water properly by removing the components (solids, deposits and suspensions) that cause damage of the injection well. One of the most effective methods of water treatment is coagulation. Aluminum(III) sulfate(VI), commonly used in coagulation, requires a neutral pH of water. Exceeding this level results in rapid reduction in coagulation efficiency, and even in increase in the content of suspended solids in purified water. Extracted reservoir waters drastically change their properties from strongly reducing to oxidizing, due to methane removal after pressure reduction and oxygenation in contact with air. Moreover, while changing the electrochemical potential to positive, presence of iron and manganese ions in the water causes precipitation of oxides and hydroxides in the form of suspensions and the pH decreases due to their hydrolysis. Due to the dynamic course of these processes, as well as the additional acidification of water by addition of the coagulant (aluminum(III) sulfate(VI)), adjustment of the pH to the level appropriate for effective coagulation is often a serious problem. The solution could be application of properly selected modern coagulants of much greater efficiency, enabling a decrease of the agent dose as well as reduction of volume and improvement of the structure of post-coagulation sediments. Additionally, they are highly efficient in a wide range of water reactions. The article describes laboratory tests on a selected coagulant (polyaluminium chloride), which allow for determination of the range of deposit water reaction in which this agent can be used. For the tests, Flokor 1ASW was selected due to its high degree of hydrolysis and slight acidity (pH ~3.5) compared with other polyaluminium chlorides, which means low consumption of total alkalinity of purified water. The results obtained show a wide range of water reaction (pH from 8.0 to 4.0), in which the effectiveness of coagulant activity ensures the correct level of purification. In addition, the use of Flokor 1ASW with effective Stabpol K flocculant allows for production of big and quickly settled flocs. Post-coagulation sediments have much smaller volume than when using aluminum(III) sulfate(VI). The results of industrial tests, carried out in order to prepare reservoir water for injection, without pH correction, have been presented in the article. They confirmed the high efficiency of the selected chemicals.