Understanding the influence of dissolved organic nitrogen characteristics on enhanced coagulation performance for water reuse

With the recent focus on using advanced water treatment processes for water reuse, interest is growing for utilizing enhanced coagulation to remove dissolved chemical species. Up to 85% of the nitrogen in wastewater effluent is made up of dissolved organic nitrogen (DON), but there is a knowledge gap regarding its removal during coagulation, which can be influenced by DON characteristics. To address this issue, tertiary-treated wastewater samples were analyzed before and after coagulation with polyaluminum chloride and ferric chloride. Samples were size-fractionated into four molecular weight fractions (0.45 μm, 0.1 μm, 10 kDa, and 3 kDa) using vacuum filtration and ultrafiltration. Each fraction was further evaluated by coagulating it separately to assess DON removal during enhanced coagulation. The size fractionated samples were also separated into hydrophilic and hydrophobic fractions using C18 solid phase extraction disks. Fluorescence excitation-emission matrices were used to investigate the characteristics of dissolved organic matter contributing to DON during the coagulation process. The results showed that DON compounds of size <3 kDa constituted a majority of the total DON. Coagulation removed more than 80% DON from size fractions 0.45 μm-0.1 μm and 0.1 μm-10 kDa, but less than 20% was removed from 10 kDa to 3 kDa and <3 kDa fractions. Coagulation on pre-filtered samples removed 19% and 25% of the <3 kDa DON fraction using polyaluminum chloride and ferric chloride, respectively. In all molecular weight fractions, hydrophilic DON compounds were found to be dominant (>90%), and enhanced coagulation was not effective in removing hydrophilic DON compounds. LMW fractions respond poorly to enhanced coagulation due to their hydrophilic nature. Enhanced coagulation effectively removes humic acid-like substances, but poorly removes proteinaceous compounds such as tyrosine and tryptophan. This study's findings provide insights into DON behavior during coagulation and factors affecting its removal, potentially improving wastewater treatment strategies.

Pilot-scale demonstration of dissolved organic nitrogen removal from an advanced water reclamation facility using enhanced coagulation

Most wastewater treatment facilities that satisfy stricter discharge restrictions for nutrients, remove dissolved inorganic nitrogen (DIN) species efficiently, leaving dissolved organic nitrogen (DON) to be present at a higher proportion (up to 85 %) of total nitrogen (TN) in the effluent. Discharged DON promotes algae growth in receiving water bodies and is a growing concern in effluent potable reuse applications considering its potential to form hazardous nitrogenous disinfection byproducts (N-DBPs). Enhanced coagulation is an established process in the advanced water treatment train for most potable reuse applications. However, so far, no information has been collected at the pilot scale to address DON removal efficiency and process implications by enhanced coagulation under real conditions. This study performed a comprehensive evaluation of DON removal from the effluent of the Truckee Meadows Water Reclamation Facility (TMWRF) by enhanced coagulation over the course of 11 months at the pilot scale. Three different coagulants (aluminum sulfate (alum), poly‑aluminum chloride (PACl), ferric chloride (FC)) and a cationic polymer coagulant aid (Clarifloc) were used. Optimum doses for each coagulant and polymer and ideal pH were determined by jar tests and applied at the pilot. Alum (24 mg/L) resulted in highly variable DON removal (6 % - 40 %, 21 % on average), which was enhanced by the addition of polymer, leading to 32 % DON removal on average. PACl (40 mg/L) and FC (100 mg/L) resulted in more consistent DON removal (on average 45 % and 57 %, respectively); however, polymer addition exerted minimal enhancement for these coagulants. Overall, enhanced coagulation effectively reduced DON in the tertiary effluent at the pilot scale. The treatment showed auxiliary benefits, including dissolved organic carbon (DOC) and orthophosphate removal.

Rates and product identification for trenbolone acetate metabolite biotransformation under aerobic conditions

Trenbolone acetate metabolites are endocrine-active contaminants discharged into the aquatic environment in runoff from agricultural fields, rangelands, and concentrated animal feeding operations. To investigate the environmental fate of these compounds and their biotransformation mechanisms, the authors used inocula from a variety of different water sources and dosed biologically active microcosms with approximately 1400 ng/L of trenbolone acetate metabolites, including 17β-trenbolone, trendione, and 17α-trenbolone. To investigate aerobic biotransformation rates and interconversions between known trenbolone acetate metabolites, gas chromatography-tandem mass spectrometry was used to measure concentrations and assess product distributions as a function of time. High-resolution liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to characterize novel transformation products and potential transformation pathways. Kinetic analysis yields observed half-lives of approximately 0.9 d, 1.3 d, and 2.2 d for 17β-trenbolone, trendione, and 17α-trenbolone, respectively, at 20 °C, although colder conditions increased half-lives to 8.5 d and biphasic transformation was observed. Relative to reported faster attenuation rates in soils, trenbolone acetate metabolites are likely more persistent in aqueous systems. Product distributions indicate an enzymatic preference for biotransformation between trendione and 17β-trenbolone. The LC-MS/MS characterization indicates dehydrogenation products as the major detectable products and demonstrates that major structural elements responsible for bioactivity in steroids are likely retained during biotransformation.

A performance evaluation of three membrane bioreactor systems: aerobic, anaerobic, and attached-growth

Water sustainability is essential for meeting human needs for drinking water and sanitation in both developing and developed countries. Reuse, decentralization, and low energy consumption are key objectives to achieve sustainability in wastewater treatment. Consideration of these objectives has led to the development of new and tailored technologies in order to balance societal needs with the protection of natural systems. Membrane bioreactors (MBRs) are one such technology. In this investigation, a comparison of MBR performance is presented. Laboratory-scale submerged aerobic MBR (AMBR), anaerobic MBR (AnMBR), and attached-growth aerobic MBR (AtMBR) systems were evaluated for treating domestic wastewater under the same operating conditions. Long-term chemical oxygen demand (COD) and total organic carbon (TOC) monitoring showed greater than 80% removal in the three systems. The AnMBR system required three months of acclimation prior to steady operation, compared to one month for the aerobic systems. The AnMBR system exhibited a constant mixed liquor suspended solids concentration at an infinite solids retention time (i.e. no solids wasting), while the aerobic MBR systems produced approximately 0.25 g of biomass per gram of COD removed. This suggests a more economical solids management associated with the AnMBR system. Critical flux experiments were performed to evaluate fouling potential of the MBR systems. Results showed similar critical flux values between the AMBR and the AnMBR systems, while the AtMBR system showed relatively higher critical flux value. This result suggests a positive role of the attached-growth media in controlling membrane fouling in MBR systems.

Evaluation of small-scale constructed wetland for water quality and Hg transformation

Elevated concentrations of nutrients and mercury (Hg) make Steamboat Creek (SBC) the most polluted tributary of the Truckee River. Since wetlands are considered cost-effective, reliable, and potential sites for methylmercury (MeHg) production, a small-scale wetland system was constructed and monitored for several years in order to quantify both nutrient removal and transformation of mercury. Results indicated seasonal variations in nutrient removal with 40-75% of total nitrogen and 30-60% of total phosphorus being removed with highest removals during summer and lowest removals during winter. The wetland system behaved as a sink for MeHg during the winter months and as a source for MeHg during summer months.

Evaluation of wetland methyl mercury export as a function of experimental manipulations

Mercury associated with natural enrichment, historic mining, and ore processing is a contaminant of concern in watersheds of the western USA. In this region, water is a highly managed resource and wetlands, known to be important sites of methyl mercury production, are often an integral component of watersheds. This study applied controlled manipulations of four replicated experimental wetland designs with different water and soil mercury concentrations to determine the potential impacts on methyl mercury export. Wetlands were manipulated by drying and wetting, changing hydraulic retention time, and adding sulfate and nitrate to influent waters. In a summer drying and wetting manipulation, an immediate increase in total methyl mercury release was observed with rewetting, however, concentrations decreased quickly. Drying all wetlands over the winter and rewetting in the spring resulted in high net methyl mercury output relative to that observed before drying. Net methyl mercury output was not influenced by changes in hydraulic retention time from 4 to 8 h or to 30 min, or by increasing the nitrate concentration from 0.1 to 10 mg L(-1). The addition of sulfate to the inlet waters of two mesocosms to increase concentrations from approximately 100 to 250 mg L(-1) did not result in a clear effect on methyl mercury output, most likely due to sulfate concentrations being higher than optimal for methyl mercury production. Despite the lack of response to sulfate amendments, the change in sulfate concentration between the inlet and outlet of the mesocosms and temperature were the parameters best correlated with methyl mercury outputs.

Modelling salinity inhibition effects during biodegradation of perchlorate

AIMS

To determine the mathematical kinetic rates and mechanisms of acclimated perchlorate (ClO)-reducing microbial cultures by incorporating a term to relate the inhibitory effect of high salinity during biological reduction of concentrated perchlorate solutions.

METHODS AND RESULTS

Salt toxicity associated with the biodegradation of concentrated perchlorate (200, 500, 1100, 1700 and 2400 mg l(-1) as ClO) was investigated using two microbial cultures isolated from a domestic wastewater treatment plant [return activated sludge (RAS) and anaerobic digester sludge (ADS)]. Experiments were performed in wastewaters containing various sodium chloride concentrations, ranging from 0% to 4.0% (w/v) NaCl (ionic strength: 0.14-0.82 mol l(-1), total dissolved solids: 5.3-42.6 g l(-1)) at near-neutral values of pH (6.7-7.8). Perchlorate biodegradation was stimulated through stepwise acclimation to high salinity. The ADS culture was capable of reducing perchlorate at salinities up to 4% NaCl, while the RAS culture exhibited complete inhibition of perchlorate degradation at 4% NaCl, probably resulting from either a toxic effect or enzyme inactivation of the perchlorate-reducing microbes. Further, a kinetic growth model was developed based on experimental data in order to express an inhibition function to relate specific growth rate and salinity.

CONCLUSIONS

Biological reduction of concentrated perchlorate wastewaters using either acclimated RAS or ADS cultures is feasible up to 3% or 4% NaCl, respectively. In addition, the kinetic model including a salinity inhibition term should be effective in many practical applications such as improving reactor design and management, furthering the understanding of high salinity inhibition, and enhancing bioremediation under high salinity loading conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Applications of these findings in water treatment practice where ion exchange or membrane technologies are used to remove perchlorate from water can have the potential to increase the overall attractiveness of these processes by eliminating the need to dispose of a concentrated perchlorate solution.

Influence of heterotrophic microbial growth on biological oxidation of pyrite

The rate and extent of pyrite oxidation by the iron-oxidizing bacteria Acidithiobacillus ferrooxidans was limited by the growth of the heterotrophic microbe Acidiphilium acidophilum. In batch systems containing a mixture of both organisms, the maximum zero-order rate of ferric iron accumulation was about 1.4 mg of Fe3+ L(-1) d(-1) as compared to 9.4 mg of Fe3+ L(-1) d(-1) for pure cultures of A. ferrooxidans under the same conditions. Pyrite oxidation was limited in cases where both cultures of organisms were initially present as well as situations where the heterotrophic organisms were added to established, pyrite-oxidizing systems containing A. ferrooxidans. Results also indicated that organic carbon remaining in solution following heterotrophic bacterial growth reduced the rate of abiotic pyrite oxidation by the ferric ion. Furthermore, a cell-free solution of the residual organic carbon resulted in a lag of A. ferrooxidans growth in soluble ferrous medium. The residual organic carbon solution that accumulated during the growth of Aph. acidophilum had a diverse molecular weight distribution, indicating that different compounds could be responsible for the inhibition of chemical pyrite oxidation and the A. ferrooxidans growth lag observed. Titration of dissolved copper ions with residual dissolved organic carbon originating from Aph. acidophilum cultures indicated that a metal complexation mechanism could be responsible for the lower rates of pyrite oxidation observed. These data suggest that encouraging the growth of heterotrophic microorganisms under acid mine drainage conditions may be a feasible strategy for decreasing both the rate and the extent of sulfide mineral oxidation.

Development and application of small-subunit rRNA probes for assessment of selected Thiobacillus species and members of the genus Acidiphilium

Culture-dependent studies have implicated sulfur-oxidizing bacteria as the causative agents of acid mine drainage and concrete corrosion in sewers. Thiobacillus species are considered the major representatives of the acid-producing bacteria in these environments. Small-subunit rRNA genes from all of the Thiobacillus and Acidiphilium species catalogued by the Ribosomal Database Project were identified and used to design oligonucleotide DNA probes. Two oligonucleotide probes were synthesized to complement variable regions of 16S rRNA in the following acidophilic bacteria: Thiobacillus ferrooxidans and T. thiooxidans (probe Thio820) and members of the genus Acidiphilium (probe Acdp821). Using (32)P radiolabels, probe specificity was characterized by hybridization dissociation temperature (T(d)) with membrane-immobilized RNA extracted from a suite of 21 strains representing three groups of bacteria. Fluorochrome-conjugated probes were evaluated for use with fluorescent in situ hybridization (FISH) at the experimentally determined T(d)s. FISH was used to identify and enumerate bacteria in laboratory reactors and environmental samples. Probing of laboratory reactors inoculated with a mixed culture of acidophilic bacteria validated the ability of the oligonucleotide probes to track specific cell numbers with time. Additionally, probing of sediments from an active acid mine drainage site in Colorado demonstrated the ability to identify numbers of active bacteria in natural environments that contain high concentrations of metals, associated precipitates, and other mineral debris.