Biodegradation rates of 2-methylisoborneol (MIB) and geosmin through sand filters and in bioreactors

Taste and odour (T&O) causing compounds, in particular, 2-methylisoborneol (MIB) and geosmin, are a problem for water authorities as they are recalcitrant to conventional water treatment. In this study, biological sand filtration was shown to be an effective process for the complete removal of MIB and geosmin, with removal shown to be predominantly through biodegradation. In addition, MIB and geosmin were also effectively degraded in batch bioreactor experiments using biofilm sourced from one of the sand filters as the microbial inoculum. The biodegradation of MIB and geosmin was determined to be a pseudo-first-order reaction with rate constants ranging between 0.10 and 0.58 d⁻¹ in the bioreactor experiments. Rate constants were shown to be dependent upon the initial concentration of the microbial inoculum but not the initial concentration of MIB and geosmin when target concentrations of 200 and 50 ng l⁻¹ were used. Furthermore, rate constants were shown to increase upon re-exposure of the biofilm to both T&O compounds. Enrichment cultures with subsequent community profile analysis using 16S rRNA-directed PCR-DGGE identified four bacteria most likely involved in the biodegradation of geosmin within the sand filters and bioreactors. These included a Pseudomonas sp., Alphaproteobacterium, Sphingomonas sp. and an Acidobacteriaceae member.     

预氯化工艺去除水中氰化物、硫化物及水合肼等还原性污染物研究

以较常见的预氯化为技术手段,考察了预氯化工艺去除饮用水中氰化物、硫化物以及水合肼等还原性污染物的效果和影响因素.结果表明:(1)实验条件下氰化物浓度随有效氯投加量的增加而下降,并在有效氯投加量＞5.0 mg/L时降低到低于《生活饮用水卫生标准》(GB5749-2006)中限值(0.05mg/L),在有效氯投加量＞6.0...     

Occurrence of THMs and HAAs in experimental chlorinated waters of the Quebec City area (Canada)

Haloacetic acids (HAAs) and trihalomethanes (THMs) were generated in bench-scale chlorination experiments using treated waters (prior to final chlorination) of the three major drinking water utilities of the Quebec City area. The purpose was to investigate the formation and occurrence of these chlorination by-products (CBPs) on a seasonal basis. Data for HAAs, THMs and other physico-chemical parameters were produced through a six-month sampling program with variable conditions of water quality, water temperature, applied chlorine dose and reaction time. In waters from the three utilities, chloroform (THM specie), dichloroacetic and trichloroacetic acid (HAA species) were the most prevalent compounds due to the low concentrations of bromide in the utilities' raw waters. Significant differences in CBP occurrence were noted between the three utilities' chlorinated waters, mainly due to the type of disinfectant applied to raw water. The use of pre-ozonation, as opposed to pre-chlorination (or direct chlorination) in one of the utilities appears to be the major factor contributing to that utility's potential for compliance with current THM and future HAA standards. Seasonal variations in THMs and HAAs were mainly associated with variations in organic precursors and to changes in water temperature (two parameters which vary widely on a seasonal basis in surface waters of southern Quebec), with CBP occurrence at its highest in spring. Statistical correlations between HAAs and THMs were moderate and only temperature appeared to affect the preponderance of one CBP or the other. Finally, a regression analysis was carried out aimed at associating each CBP to water quality and the experimental parameters. Thanks to their predictive ability, multivariate models seem to be the tools with the best potential for decision-making purposes.     

活性炭柱中砂垫层在微污染水源水处理工艺中的应用

以嘉兴市某水厂沉后水为进水进行实验,研究炭砂滤池对污染物的去除性能,以及炭砂滤池取代活性炭＋砂滤池的可能性,探讨了短流程工艺的适用性。结果表明,炭砂滤池能有效去除水中的浊度、氨氮、CODMn和铁、锰等污染物,与活性炭柱相比,炭砂滤池在降低出水浊度和水中颗粒数方面具有一定优势,即砂垫层对控制出水浊度和保障微生物安全能够起到积极作用。在实验条件下,增加活性炭层厚度或者降低滤速,在一定程度上有利于提高对CODMn的去除率。在设计滤速为9～10 m/h,CODMn〈4.5 mg/L时,可直接以炭砂滤池取代活性炭池＋砂滤池,仍然能保证出水CODMn〈3 mg/L。     

Factors influencing formation of trihalomethanes in drinking water with special reference to Swedish conditions

The trihalomethane (THM) concentrations in drinking water are greatly affected by the disinfection methods as well as the organic content of the water. The THM formation was shown to increase considerable during 24 hours. This indicates a higher concentration of THM at the consumers' tap compared to the levels in the outgoing water from the water work. The dosage ratio between chlorine and ammonium sulphate can be used to regulate the THM concentrations. Disinfection with a relatively high dosage of chlorine dramatically increase the THM level while the equal amount of chlorine dioxide produces trace concentrations of THM only. The relatively low THM concentrations in Swedish drinking water as compared to levels found in water from for example the USA may probably depend on the low chlorine dosage practiced in Sweden.     

Nano-silver in drinking water and drinking water sources: stability and influences on disinfection by-product formation

Nano-silver is increasingly used in consumer products from washing machines and refrigerators to devices marketed for the disinfection of drinking water or recreational water. The nano-silver in these products may be released, ending up in surface water bodies which may be used as drinking water sources. Little information is available about the stability of the nano-silver in sources of drinking water, its fate during drinking water disinfection processes, and its interaction with disinfection agents and disinfection by-products (DBPs). This study aims to investigate the stability of nano-silver in drinking water sources and in the finished drinking water when chlorine and chloramines are used for disinfection and to observe changes in the composition of DBPs formed when nano-silver is present in the source water. A dispersion of nano-silver particles (10 nm; PVP-coated) was used to spike untreated Ottawa River water, treated Ottawa River water, organic-free water, and a groundwater at concentrations of 5 mg/L. The diluted dispersions were kept under stirred and non-stirred conditions for up to 9 months and analyzed weekly using UV absorption to assess the stability of the nano-silver particles. In a separate experiment, Ottawa River water containing nano-silver particles (at 0.1 and 1 mg/L concentration, respectively) was disinfected by adding sodium hypochlorite (a chlorinating agent) in sufficient amounts to maintain a free chlorine residual of approximately 0.4 mg/L after 24 h. The disinfected drinking water was then quenched with ascorbic acid and analyzed for 34 neutral DBPs (trihalomethanes, haloacetonitriles, haloacetaldehydes, 1,1 dichloro-2-propanone, 1,1,1 trichloro-2-propanone, chloropicrin, and cyanogen chloride). The results were compared to the profile of DBPs obtained under the same conditions in the absence of nano-silver and in the presence of an equivalent concentration of Ag⁺ ions (as AgNO₃). The stability of the nano-silver dispersions in untreated Ottawa River water, with a dissolved organic carbon concentration of 6 mg/L, was significantly higher than the stability of the nano-silver dispersions in distilled, organic-free water. Nano-silver particles suspended in the groundwater agglomerated and were quickly and quantitatively removed from the solution. Our data confirm previous observations that natural dissolved organic matter stabilizes nano-silver particles, while the high-ionic strength of groundwater appears to favor their agglomeration and precipitation. As expected, nano-silver was not stable in Ottawa River water through the chlorination process, but survived for many days when added to the Ottawa River water after treatment with chlorine or chloramines. Stirring appeared to have minimal effect on nano-silver stability in untreated and treated Ottawa River water. The profile of DBPs formed in the presence of nAg differed significantly from the profile of DBPs formed in the absence of nAg only at the 1 mg/L nAg concentration. The differences observed consisted mainly in reduced formation of some brominated DBPs and a small increase in the formation of cyanogen chloride. The reduced formation of brominated congeners may be explained by the decrease in available bromide due to the presence of Ag⁺ ions. It should be noted that a concentration of 1 mg/L is significantly higher than nAg concentrations that would be expected to be present in surface waters, but these results could be significant for the disinfection of some wastewaters with comparably high nano-silver concentrations.     

Disinfection by-products in Finnish drinking waters

Disinfection by-products (DBPs) were measured in plant effluents of 35 Finnish waterworks, which utilized different treatment processes and raw water sources. DBPs were measured also from the distribution systems of three waterworks. Di- and trichloroacetic acids, and chloroform were the major DBPs found in treated water samples. The concentration of six haloacetic acids (HAA6) exceeded the concentrations of trihalomethanes (THMs). Chlorinated drinking waters (DWs) originating from surface waters contained the highest concentration of HAA6 and THMs: 108 and 26 microg/l, respectively. The lowest concentrations of DBPs were measured from ozonated and/or activated carbon filtrated and chloraminated DWs. Higher concentrations of HAA6, THMs, and adsorbable organic halogens were measured in summer compared to winter. The levels of chlorinated acetic acids, chloroform, and bromodichloromethane correlated positively with mutagenicity. Past mutagenicity levels of DWs were examined. A major reduction in the use of prechlorination, increased use of chloramine disinfection, and better removal of organic carbon were the most important reasons for the 69% decrease in mutagenicity from 1985 to 1994.     

Haloacetic acid removal by sequential zero-valent iron reduction and biologically active carbon degradation

An innovative haloacetic acid (HAA) removal process was developed. The process consisted of a zero-valent iron (Fe⁰) column followed by a biologically active carbon (BAC) column that were efficient in degrading tri- and di-HAAs, and mono- and di-HAAs, respectively. The merit of the process was demonstrated by its performance in removing trichloroacetic acid (TCAA). An empty bed contact time of 10 min achieved nearly complete removal of 1.2 μM TCAA and its subsequent products, dichloroacetic acid (DCAA) and monochloroacetic acid (MCAA). HAA removal was a result of chemical dehalogenation and biodegradation rather than physical adsorption. Preliminary kinetic analyses were conducted and the pseudo-first-order rate constants were estimated at ambient conditions for Fe⁰ reduction of TCAA and biodegradation of DCAA and MCAA by BAC. This innovative process is highly promising in removing HAAs from drinking water, swimming pool water, and domestic or industrial wastewater.     

Biodegradation of haloacetic acids by bacterial enrichment cultures

Haloacetic acids (HAAs) are toxic organic chemicals that are frequently detected in surface waters and in drinking water distribution systems. The aerobic biodegradation of HAAs was investigated in serum bottles containing a single HAA and inoculated with washed microorganisms obtained from enrichment cultures maintained on either monochloroacetic acid (MCAA) or trichloroacetic acid (TCAA) as the sole carbon and energy source. Biodegradation was observed for each of the HAAs tested at concentrations similar to those found in surface waters and in drinking water distribution systems. The MCAA culture was able to degrade both MCAA and monobromoacetic acid (MBAA) with pseudo-first order rate constants of 1.06 x 10(-2) and 1.13 x 10(-2) l(mg protein)(-1) d(-1), respectively, for concentrations ranging from 10(-5) to 2 mM. The pseudo-first order rate constant for TCAA degradation by the TCAA culture was 6.52 x 10(-3) l(mg protein)(-1) d(-1) for concentrations ranging from 5.33 x 10(-5) to 0.72 mM. The TCAA culture was also able to degrade MCAA with the rate accelerating as incubation time increased. Experiments with radiolabeled HAAs indicated that the 14C was primarily converted to 14CO2 with minor incorporation into cell biomass. The community structure of the enrichment cultures was analyzed by both cultivation-dependent and cultivation-independent approaches. Denaturing gradient gel electrophoresis (DGGE) of the PCR-amplified 16S rRNA gene fragments showed that each of the two enrichment cultures had multiple bacterial populations, none of which corresponded to HAA-degrading bacteria cultivated on HAA-supplemented agar plates. This research indicates that biodegradation is a potential loss mechanism for HAAs in surface waters and in drinking water distribution systems.     

Gaseous Ammonia Uptake in Compost Biofilters as Related to Compost Water Content

Abstract

Sewage sludge and yard waste compost were used as biofilter materials and tested with respect to their capacity for removing ammonia from air at different water contents. Ammonia removal was measured in biofilters containing compost wetted to different moisture contents ranging from air dry to field capacity (maximum water holding capacity). Filters were operated for 15 days and subsequently analyzed for NH₃/NH₄ ⁺, NO₂ ^-, and NO₃ ^-. The measured nitrogen species concentration profiles inside the filters were used to calculate ammonia removal rates. The results showed that ammonia removal is strongly dependent on the water content in the filter material. At gravimetric water contents below 0.25 g H₂O g solids^-1 for the yard waste compost and 0.5 g H₂O g solids^-1 ammonia removal rates were very low but increased rapidly above these values. The sewage sludge compost filters yielded more than twice the ammonia removal rate observed for yard waste compost likely because of a high initial concentration of nitrifying bacteria originating from the wastewater treatment process and a high air-water interphase surface area that facilitates effective ammonia dissolution and transport to the biofilm.     

Effect of ozonation on the biodegradability of atrazine in GAC columns

Abstract

The biodegradation of atrazine as influenced by preozonation was studied in biological GAC columns. Metabolism of isopropyl‐¹⁴C atrazine produced more ¹⁴CO₂ than ring‐UL‐¹⁴C atrazine, indicating dealkylation was more rapid than ring cleavage. Preozonation increased mineralization of ring‐UL‐¹⁴C atrazine and, consequently, enhanced the performance of the GAC columns. Sixty‐two percent of the influent atrazine was converted to ¹⁴CO₂ in columns that received ozonated atrazine and ozonated surface water, while 50% of the influent atrazine was converted to ¹⁴CO₂ in columns that received untreated atrazine and ozonated surface water, and only 38% of the influent atrazine was converted to ¹⁴CO₂ in columns with untreated influent.     

Minimization of the formation of disinfection by-products

The drinking water industry is required to minimize DBPs levels while ensuring adequate disinfection. In this study, efficient and appropriate treatment scheme for the reduction of disinfection by-product (DBPs) formation in drinking water containing natural organic matter has been established. This was carried out by the investigation of different treatment schemes consisting of enhanced coagulation, sedimentation, disinfection by using chlorine dioxide/ozone, filtration by sand filter, or granular activated carbon (GAC). Bench scale treatment schemes were applied on actual samples from different selected sites to identify the best conditions for the treatment of water. Samples were collected from effluent of each step in the treatment train in order to analyze pH, UV absorbance at 254 nm (UVA₂₅₄), specific UV absorbance at 254 nm (SUVA₂₅₄), dissolved organic carbon (DOC), haloacetic acids (HAAs) and trihalomethanes (THMs). The obtained results indicated that using pre-ozonation/enhanced coagulation/activated carbon filtration treatment train appears to be the most effective method for reducing DBPs precursors in drinking water treatment.     

Formation of Disinfection Byproducts (DBPs) in Surface Water Sources: Differential Ultraviolet (UV) Absorbance Approach

Chlorination for drinking water forms various disinfection byproducts (DBPs) of trihalomethanes (THMs) and haloacetic acids (HAAs). Chlorination has been attributed to the destruction of activated aromatic sites of the natural organic matter (NOM) predominantly at electron rich sites. Experiments with Istanbul surface waters showed that the magnitude of the decrease in the ultraviolet (UV) absorbance at 272 nm (UV₂₇₂) was an excellent indicator of destruction of these sites by chlorine. The main objective of the present study is to develop the differential UV₂₇₂ absorbance (ΔUV₂₇₂) related models for the prediction of the formation of THM, HAA, and their species in raw water samples from Terkos, Buyukcekmece, and Omerli lakes under different chlorination conditions. Significant factors affecting DBP formation in the raw waters were identified through numerical and graphical techniques. The R² values of the models varied between 0.94 and 0.97, indicating excellent predictive ability for THM₄ and HAA₉ in the raw waters. The models were validated using additional data. The results of this study concluded that addition of ΔUV₂₇₂ parameter into THM₄ and HAA₉ models make the prediction of these DBP compounds more precisely than those of DBP models developed in the past. A better understanding of these modeling systems will help the water treatment plant operators to minimize the DBP formation, providing a healthier and better drinking water quality as well as identifying strategies to improve water treatment and disinfection processes.     

Water quality performance of a batch-type stormwater detention basin.

The objective of this research was to modify an extended detention basin to provide batch treatment of stormwater runoff. An automated valve/controller was developed and placed on the outlet of a detention basin in Austin, Texas, which allowed the water quality volume to be retained in the basin for a preset length of time. The influent and effluent of the modified basin were monitored for total suspended solids (TSS), nutrients, chemical oxygen demand (COD), and total and dissolved metals. Statistically significant removal of total metals, COD, total nitrogen, total phosphorus, and TSS was observed, with a discharge event mean TSS concentration of 7 mg/L and a TSS removal efficiency of 91%. The modified basin has substantially better pollutant removal than conventional extended detention basins and is comparable with that of Austin sand filters, which are a common structural stormwater treatment system in the Austin area. The valve also can be used to isolate hazardous material spills.     

Combined use of molecular biology taxonomy, Raman spectrometry, and ESEM imaging to study natural biofilms grown on filter materials at waterworks

DNA-based population analysis was applied in combination with Raman spectrometry and Environmental Scanning Electron Microscopy for the characterisation of natural biofilms from sand and activated carbon filters operated for a long term at a municipal waterworks. Whereas the molecular biology polymerase chain reaction combined with denaturing gradient gel electrophoresis approach provides a deeper insight into the bacterial biofilm diversities, Raman spectrometry analyses the chemical composition of the extracellular polymer substances (EPS), microorganisms embedded in EPS as well as other substances inside biofilm (inorganic compounds and humic substances). Microscopy images the spatial distribution of biofilms on the two different filter materials. In addition, bacterial bulk water populations were compared with biofilm consortia using the molecular fingerprint technique mentioned.Population analysis demonstrated the presence of more diverse bacterial species embedded in a matrix of EPS (polysaccharides, peptides, and nucleic acids) on the sand filter materials. In contrast to this, activated carbon granules were colonised by reduced numbers of bacterial species in biofilms. Besides α-, β-, and γ-Proteobacteria, a noticeable specific colonisation with Actinobacteria was found on activated carbon particles. Here, the reduced biofilm formation came along with a decreased EPS synthesis. The taxonomy profiles of the different biofilms revealed up to 60% similarity on the same filter materials and 32% similarity of different materials. Similarity of adherent communities from filter materials and bulk water populations from the filter effluent varied between 36% and 58% in sand filters and 6–40% in granular activated carbon filters.The biofilm investigation protocols are most crucial to subsequent acquisition of knowledge on biofilm dynamics and bacterial contributions to transformation or adsorption processes in waterworks facilities.     

Performance comparison of structural stormwater best management practices.

This paper describes a method for comparing the pollutant removal of a number of structural stormwater treatment devices, commonly referred to as best management practices (BMPs). Historically, the pollutant removal ability of a BMP has been expressed as a percent reduction in concentration or load. Unfortunately, the calculated percent reduction in pollutant concentration is strongly affected by the influent concentration, with the calculated reduction generally being much lower when the event mean concentrations (EMCs) in the untreated runoff from the test watershed are low. The objective of the proposed methodology is to eliminate this problem by predicting BMP performance for an arbitrary influent concentration, so that BMPs evaluated in different watersheds can be compared as if the influent quality at all sites were the same. This method allows BMPs to be compared based on the quality of effluent produced and the mass reduction. The proposed method uses linear regression as the primary tool to compute the expected effluent concentration from a BMP, given a specific influent concentration of interest and was developed using data collected in the California Department of Transportation BMP Retrofit Pilot Program. This technique reveals that for media filters, the concentration of sediment and other particle-associated pollutants in treated runoff is generally unrelated to influent quality and is relatively constant. Wet basins with large permanent pool volumes also have effluent concentrations that are constant for most constituents and unrelated to influent concentrations. In these situations, the "percent reduction" in a pollutant EMC is not an inherent characteristic of the BMP, but a function of the influent EMC, because the quality of effluent produced is constant. Predicting the effluent quality of several types of conventional BMPs based on a common influent concentration allows an objective comparison of their performance and the selection of a BMP that addresses specific constituents of concern.     

Biotrickling Filtration of Nitric Oxide

ABSTRACT

A biotrickling filter with blast-furnace slag packings (sizes = 20-40 mm and specific surface area = 120 m²/m³) was utilized to treat NO in an air stream. The operational stability, as well as the effects of gas empty-bed retention time (EBRT) and nutrient addition on the removal ability of NO, were tested. Approximately six weeks were required for the development of a biofilm for NO degradation, and a two-week organic carbon deficiency resulted in the detachment of biofilms from the packing surfaces. A steady removal rate of 80% was attained at specified influent NO concentrations of 892 to 1237 ppm and an EBRT of 118 sec. The effluent NO concentration diminished exponentially with enlarging EBRT, with influent NO concentrations of 203-898 ppm, and EBRTs of 25 to 118 sec. Nutrient addition is essential for efficient removal of the influent NO. Mass ratios of C: P: N = 7: 1: 30 and NaHCO₃: NO-N = 6.3 could be used for practical applications.     

紫外线杀菌效能的研究

自来水的消毒目前普遍采用氯及含氯化合物药剂，消毒过程中产生三卤甲烷等致癌或致突变物质，从而造成水体的二次污染，许多国家已经禁止在消毒中使用含氯药剂。因此，具有安全可靠高效杀菌作用的紫外线消毒技术逐渐发展起来，并越来越受到人们的关注。但是紫外线的使用也有一定的限制，通过紫外线照射时间及进水浊度的变化，研究了具有一定照射强度的紫外灯的杀菌效能变化，并得出了紫外线具有最佳杀菌效果的进水极限浊度和照射时间。同时还研究了紫外线对具有不同抗性的细菌的系灭效率，为饮用水和污水的消毒处理提供了实验基础。     

自来水二氧化氯消毒控制三氯甲烷研究

对自来水二氧化氯消毒控制三氯甲烷形成进行了试验研究 ,二氧化氯预消毒替代预氯化消毒可以降低水中的三氯甲烷 ,预消毒处理后形成三氯甲烷的反应受温度和反应时间的影响。使用二氧化氯与氯配制的混合消毒剂消毒时 ,随二氧化氯含量增加 ,水中的三氯甲烷将明显减少。     

不同填料载体生物膜对微囊藻毒素的去除效果

利用自行设计的生物膜培养装置,通过对4种不同填料载体进行连续曝气循环培养生物膜,对湖水中的溶解态微囊藻毒素(MCs)的去除作用进行了研究。结果表明,填料载体上生物膜从形成到稳定大约需要3周;生物膜形成后对MCs的去除效率由高到低的顺序是:颗粒活性炭柱>多密孔球型滤料柱>塑料悬浮填料柱>陶瓷滤球柱。在实验水质条件下,当水力停留时间(HRT)=5 h,进水MCs浓度为21.5～47.25μg/L时,颗粒活性炭、多密孔球型滤料柱对MCs的去除率最高可达100%,塑料悬浮填料柱对MC-LR和MC-RR的去除率分别为70%和88%。当HRT=2.5 h时,塑料悬浮填料柱对MC-RR的去除率为MC-LR的2倍。生物膜对MCs的降解效果随温度(5～20℃)和溶解氧的升高而增加。塑料悬浮填料作为合适的生物膜挂膜填料载体对水源水的生物预处理具有良好的应用前景。