The significance of colloids in the transport of pesticides through Chalk

Agrochemical contamination in groundwater poses a significant long term threat to water quality and is of concern for legislators, water utilities and consumers alike. In the dual porosity, dual permeability aquifers such as the Chalk aquifer, movement of pesticides and their metabolites through the unsaturated zone to groundwater is generally considered to be through one of two pathways; a rapid by-pass flow and a slower 'piston-flow' route via the rock matrix. However, the dissolved form or 'colloidal species' in which pesticides move within the water body is poorly understood. Following heavy rainfall, very high peaks in pesticide concentration have been observed in shallow Chalk aquifers. These concentrations might be well explained by colloidal transport of pesticides. We have sampled a Chalk groundwater beneath a deep (30 m) unsaturated zone known to be contaminated with the pesticide diuron. Using a tangential flow filtration technique we have produced colloidal fractions from 0.45 microm to 1 kDa. In addition, we have applied agricultural grade diuron to a typical Chalk soil and created a soil water suspension which was also subsequently fractionated using the same filtration system. The deep groundwater sample showed no evidence of association between colloidal material and pesticide concentration. In comparison, despite some evidence of particle trapping or sorption to the filters, the soil water clearly showed an association between the <0.45 microm and <0.1 microm colloidal fractions which displayed significantly higher pesticide concentrations than the unfiltered sample. Degradation products were also observed and found to behave in a similar manner to the parent compound. Although relatively large colloids can be generated in the Chalk soil zone, it appears transport to depth in a colloidal-bound form does not occur. Comparison with other field and monitoring studies suggests that rapid by-pass flow is unlikely to occur beneath 4-5 m. Therefore, shallow groundwaters are most at risk from rapid transport of high concentrations of pesticide-colloidal complexes. The presence of a deep unsaturated zone will mean that most of the colloidal-complexes will be filtered by the narrow Chalk pores and the majority of pesticide transport will occur in a 'dissolved' form through the more gradual 'piston-flow' route.     

Microbial contamination of two urban sandstone aquifers in the UK

Development of urban groundwater has historically been constrained by concerns about its quality. Rising urban water tables and overabstraction from rural aquifers in the UK have led to a renewed interest in urban groundwater, particularly the possibility of finding water of acceptable quality at depth. This study assessed the microbial quality of groundwater collected from depth-specific intervals over a 15-month period within the Permo-Triassic Sherwood Sandstone aquifers underlying the cities of Nottingham and Birmingham. Sewage-derived bacteria (thermotolerant coliforms, faecal streptococci and sulphite-reducing clostridia) and viruses (enteroviruses, Norwalk-like viruses, coliphage) were regularly detected to depths of 60 m in the unconfined sandstone and to a depth of 91 m in the confined sandstone. Microbial concentrations varied temporally and spatially but increased frequency of contamination with depth coincided with geological heterogeneities such as fissures and mudstone bands. Significantly, detection of Norwalk-like viruses and Coxsackievirus B4 in groundwater corresponded with seasonal variations in virus discharge to the sewer system. The observation of low levels of sewage-derived microbial contaminants at depth in the Triassic Sandstone aquifer is explained by the movement of infinitesimal proportions of bulk (macroscopic) groundwater flow along preferential pathways (e.g., fissures, bedding planes). The existence of very high microbial populations at source (raw sewage) and their extremely low detection limits at the receptor (multilevel piezometer) enable these statistically extreme (microscopic) flows to be traced. Rapid penetration of microbial contaminants into sandstone aquifers, not previously reported, highlights the vulnerability of sandstone aquifers to microbial contamination.     

Groundwater Pollution Arising from the Disposal of Creosote Waste

Creosote-contaminated groundwater contains a complex mixture of phenols, aromatic hydrocarbons and nitrogen-, sulphur- or oxygen-containing heterocyclic, aromatic compounds. One of the most important factors that limits the spreading of these contaminants in groundwater aquifers is degradation by subsurface micro-organisms.
This paper gives an overview of the present knowledge about microbial degradation of creosote contaminants under aerobic and anaerobic conditions. Furthermore, various techniques for biological remediation of creosote-contaminated groundwater are outlined. These techniques include enhancement of the native population of subsurface micro-organisms to degrade the contaminants ( in situ treatment) and withdrawal of the groundwater followed by treatment by various wastewater treatment processes (above-ground treatment).     

Nutrient gradients in a granular activated carbon biofilter drives bacterial community organization and dynamics

The quality of drinking water is ensured by hygienic barriers and filtration steps, such as ozonation and granular activated carbon (GAC) filtration. Apart from adsorption, GAC filtration involves microbial processes that remove biodegradable organic carbon from the ozonated ground or surface water and ensures biological stability of the treated water. In this study, microbial community dynamics in were monitored during the start-up and maturation of an undisturbed pilot-scale GAC filter at 4 depths (10, 45, 80 and 115 cm) over a period of 6 months. New ecological tools, based on 16S rRNA gene-DGGE, were correlated to filter performance and microbial activity and showed that the microbial gradients developing in the filter was of importance. At 10 cm from the top, receiving the freshly ozonated water with the highest concentration of nutrients, the microbial community dynamics were minimal and the species richness remained low. However, the GAC samples at 80-115 cm showed a 2-3 times higher species richness than the 10-45 cm samples. The highest biomass densities were observed at 45-80 cm, which corresponded with maximum removal of dissolved and assimilable organic carbon. Furthermore, the start-up period was clearly distinguishable using the Lorenz analysis, as after 80 days, the microbial community shifted to an apparent steady-state condition with increased evenness. This study showed that GAC biofilter performance is not necessarily correlated to biomass concentration, but rather that an elevated functionality can be the result of increased microbial community richness, evenness and dynamics.     

Extracellular enzyme activities during slow sand filtration in a water recharge plant

Activities of the extracellular enzymes beta-glucosidase and phosphatase and bacterial densities were investigated during the filtration process at several sites in a groundwater recharge plant at the Ruhr river (Hengsen recharge plant in Schwerte. Germany). Low numbers of microorganisms and low levels of activity in this type of habitat, compared to most surface waters, caused methodological problems when determining microbial activity. In this study, fluorigenic model substrates, which enable hydrolytic rates as low as 1 nmol (L x h)(-1) to be measured, were used to determine extracellular enzyme activities. Highest activities were determined in surface water (107 nmol (L x h)(-1) for beta-glucosidase and 252 nmol (L x h)(-1) for phosphatase). which decreased during the filtration process in the gravel prefilter and the main sand filter until the end of subsurface flow (1.6 nmol (L x h)(-1) and 6.8 nmol (L x h)(-1), respectively). Similarly, bacterial numbers decreased from 3.4 x 10(6) to 0.29 x 10(6) cells mL(-1). These data showed that microbial activity within the prefilter and the shallow layers of the sand filter had the greatest impact on water quality. In addition to its involvement in the continuous purification of surface water, the microbial community in the sand filter probably acts as a biological buffer against ephemeral increases in the loads of organic matter and nutrients in the recharge plant.     

Comparative microscale analysis of the effects of triclosan and triclocarban on the structure and function of river biofilm communities

The broad spectrum antimicrobials triclosan (TCS) and triclocarban (TCC) are commonly detected in the environment. However, there is very limited understanding of the aquatic ecological implications of these agents. During this study, river biofilms were cultivated using 10 µg l^− 1 of TCS or TCC and the equivalent in nutrients (carbon, nitrogen) over a developmental period of 8 weeks. Confocal laser microscopy showed that the biofilm communities developing under the influence of TCS and TCC had community architecture and composition different from either control or nutrient exposed communities. Microscale analyses of biofilm community structure indicated a significant reduction in algal biomass (p < 0.05) as a result of exposure to either TCS or TCC. Thymidine incorporation did not detect significant differences between control and treated communities. The use of carbon utilization assays based on growth indicated that, in general, TCS and TCC suppressed utilization. The community was altered from one dominated by autotrophic processes to one dominated by heterotrophic processes. Both TCS and TCC treatments resulted in significant (p < 0.05) alterations in the composition of the EPS matrix of the communities, suggesting significant changes in community composition. Denaturing gradient gel electrophoresis and PCA-ANOSIM analyses indicated a significant change occurred in the bacterial community as a consequence of TCS treatments. Enumeration of micrometazoa and protozoa revealed an increase in micrometazoan numbers over control values, whereas no clear impact on protozoa was detected in any treatment. This study indicated significant effects of 10 µg l^− 1 TCS and TCC on microbial community composition, algal biomass, architecture and activity.     

Arsenic removal from high-arsenic water by enhanced coagulation with ferric ions and coarse calcite

Arsenic removal from high-arsenic water in a mine drainage system has been studied through an enhanced coagulation process with ferric ions and coarse calcite (38-74 microm) in this work. The experimental results have shown that arsenic-borne coagulates produced by coagulation with ferric ions alone were very fine, so micro-filtration (membrane as filter medium) was needed to remove the coagulates from water. In the presence of coarse calcite, small arsenic-borne coagulates coated on coarse calcite surfaces, leading the settling rate of the coagulates to considerably increase. The enhanced coagulation followed by conventional filtration (filter paper as filter medium) achieved a very high arsenic removal (over 99%) from high-arsenic water (5mg/l arsenic concentration), producing a cleaned water with the residual arsenic concentration of 13 microg/l. It has been found that the mechanism by which coarse calcite enhanced the coagulation of high-arsenic water might be due to attractive electrical double layer interaction between small arsenic-borne coagulates and calcite particles, which leads to non-existence of a potential energy barrier between the heterogeneous particles.     

Experiences of Biological Iron and Manganese Removal in Finland

Even though groundwater resources in Finland are adequate, and theoretically the total water consumption could be supplied from this source, in practice only about 50% of the total consumption is from groundwater. There are thousands of unconnected small aquifers dispersed all over the country, and the use of these as water supplies is not economically possible.
Biological iron and manganese removal systems appear to be a promising alternative to chemical treatment. In Finland the following biological treatment systems are in use: (i) VYREDOX method; (ii) overland flow method; (iii) slow sand filtration; (iv) re-infiltration; and (v) biological reactors.
Active iron and manganese bacteria play the most essential role in all these applications, and different methods of removal are discussed in detail in the paper.     

Significance of biomass support particles in laboratory studies on microbial degradation of organic chemicals in aquifers

In degradation studies of xenobiotics in groundwater environments from where only water samples can be obtained (e.g. established deep groundwater wells, inhomogeneous formations as boulder aquifers, or consolidated aquifers), solids might be added as biomass support materials. The importance of biomass support materials as quartz sand, rock wool and crushed tiles on the degradation of 8 aromatic hydrocarbons (benzene, toluene, o-xylene, 1,2-dichlorobenzene (1,2-DCB), 1,4-dichlorobenzene (1,4-DCB), naphthalene, biphenyl and nitrobenzene) was investigated in experiments with groundwater collected from two aerobic aquifers (Vejen and Grindsted, Denmark). Experiments with only groundwater as well as groundwater suspensions with aquifer sediment were run as references. It was impossible to adjust pH to the desired level in the experiments with crushed tiles, where also substantial sorption of the test compounds and server clogging of filters used in sampling occurred, and this material was therefore useless as biomass support material. Presence of rock wool supported growth of bacteria and increased the degradation (in terms of rates and number of compounds degraded) compared with experiments with groundwater only. However, the degradation was less and the degradation patterns varied more than in the presence of aquifer sediment. Quartz sand gave the most promising results with respect to growth of bacteria, and the degradation patterns of most of the compounds were similar to those obtained in experiments including aquifer sediments, although the latter showed the most substantial degradation. This study suggests that in case aquifer sediment is not available, quartz sand should be added as biomass support material in studies on degradation of organic xenobiotics in groundwater environments.     

Treatment of fish-processing wastewater by co-culture of Candida rugopelliculosa and Brachionus plicatilis

This research was conducted as a part of the continuous development of a novel technique for managing fish-processing wastewater by cultivating proteolytic yeast, Candida rugopelliculosa, as possible diet of the rotifer, Brachionus plicatilis. It was feasible to use Alaska Pollack processing wastewater as a growth medium for C. rugopelliculosa, which was stimulatory for growth of the rotifer by 18.3% over the commercial diet of Saccharomyces cerevisiae. Maximum growth of C. rugopelliculosa and reduction of influent soluble chemical oxygen demand (SCOD) concentration were respectively (6.09+/-0.04)x10(6) cells/ml and 70.0% at 6.3h hydraulic retention time (HRT).Method of 4th order Runge-Kutta approximation was successfully applied to determine the Monod kinetics of C. rugopelliculosa by using unsteady state data from only one continuous unsteady state operation at a fixed HRT. The maximum microbial growth rates, mu(max), and half saturation coefficient, K(s), were determined to be 0.82+/-0.22 h(-1) and 690+/-220 mg SCOD/L, respectively. The microbial yield coefficient, Y, and microbial decay rate coefficient, k(d), were determined to be (1.39+/-0.22)x10(4) cells/mg SCOD and 0.06+/-0.01 h(-1), respectively.     

Influence of filtration on concentrations of 62 elements analysed on crystalline bedrock groundwater samples by ICP-MS.

Analyses of unfiltered and filtered (< 0.45 micron and < 0.10 micron) groundwater samples from 15 selected wells in crystalline bedrock aquifers of the Oslo area, Norway, have been studied for 62 chemical elements. While concentrations of almost all elements vary over several orders of magnitude between the individual wells, the discrepancy between filtered and unfiltered samples from the same well are rather small, not exceeding one order of magnitude. Many elements show no influence of filtration at all, while one element (Sn) suggests that filtration may actually introduce contamination to the samples. Correlation between unfiltered and filtered samples is high for most elements. The study shows that: (1) even unfiltered samples will satisfactorily reflect general water chemistry as long as drinking water (i.e. by definition rather 'clean' water, with low particulates) is collected; (2) filtered samples do not necessarily reflect 'true' solution chemistry (an elusive concept); and (3) the differences between samples filtered at < 0.45 micron and < 0.10 micron are so minimal for most elements, that the additional effort invested in ultra-filtration may not be justified for bedrock groundwater samples.     

Spatial and temporal changes in Actinobacterial dominance in experimental artificial groundwater recharge

Artificial groundwater recharge (AGR) is used in the drinking water industry to supplement groundwater resources and to minimise the use of chemicals in water treatment. This study analysed the spatial and temporal changes of microbial communities in AGR using two test systems: a nutrient-amended fluidized-bed reactor (FBR) and a sand column. Structural changes in the feed lake water (Lake Roine), FBR, and sand column bacterial communities were determined by denaturing gradient gel electrophoresis (DGGE) and the length heterogeneity analysis of amplified 16S rRNA genes (LH-PCR). Two clone libraries were created to link the LH-PCR results to the dominant bacterial groups. The lake water bacterial community was relatively stable, with three bands dominating in all LH-PCR products. The most dominant fragment accounted for up to 72% and was derived from Actinobacteria. Based on the clone libraries and LH-PCR data, Actinobacteria also dominated in the unattached bacterial community of the FBR, whereas several Proteobacterial groups were more abundant on the FBR carrier particles. In the stabilised AGR system a major change in the community structure of the lake water bacteria took place during passage within the first 0.6 m in the sand column as the community composition shifted from Actinobacteria-dominated populations to a diverse, mainly Proteobacterial communities. Concurrently, most of the dissolved organic carbon (DOC) was removed at this stage. In summary, the study showed that the make-up of microbial communities in experimental AGR systems responded to changes in their environment. LH-PCR showed potential as a method to determine microbial community dynamics in long-term studies at real-scale AGR sites. This is the first step to provide data on microbial community dynamics in AGR for drinking water production.     

Measurement and interpretation of microbial adenosine tri-phosphate (ATP) in aquatic environments

There is a widespread need for cultivation-free methods to quantify viability of natural microbial communities in aquatic environments. Adenosine tri-phosphate (ATP) is the energy currency of all living cells, and therefore a useful indicator of viability. A luminescence-based ATP kit/protocol was optimised in order to detect ATP concentrations as low as 0.0001 nM with a standard deviation of <5%. Using this method, more than 100 water samples from a variety of aquatic environments (drinking water, groundwater, bottled water, river water, lake water and wastewater effluent) were analysed for extracellular ATP and microbial ATP in comparison with flow-cytometric (FCM) parameters. Microbial ATP concentrations ranged between 3% and 97% of total ATP concentrations, and correlated well (R² = 0.8) with the concentrations of intact microbial cells (after staining with propidium iodide). From this correlation, we calculated an average ATP-per-cell value of 1.75 × 10⁻¹⁰ nmol/cell. An even better correlation (R² = 0.88) was observed between intact biovolume (derived from FCM scatter data) and microbial ATP concentrations, and an average ATP-per-biovolume value of 2.95 × 10⁻⁹ nmol/μm³ was calculated. These results support the use of ATP analysis for both routine monitoring and research purposes, and contribute towards a better interpretation of ATP data.     

Nitrate attenuation in groundwater: a review of biogeochemical controlling processes

Biogeochemical processes controlling nitrate attenuation in aquifers are critically reviewed. An understanding of the fate of nitrate in groundwater is vital for managing risks associated with nitrate pollution, and to safeguard groundwater supplies and groundwater-dependent surface waters. Denitrification is focused upon as the dominant nitrate attenuation process in groundwater. As denitrifying bacteria are essentially ubiquitous in the subsurface, the critical limiting factors are oxygen and electron donor concentration and availability. Variability in other environmental conditions such as nitrate concentration, nutrient availability, pH, temperature, presence of toxins and microbial acclimation appears to be less important, exerting only secondary influences on denitrification rates. Other nitrate depletion mechanisms such as dissimilatory nitrate reduction to ammonium and assimilation of nitrate into microbial biomass are unlikely to be important in most subsurface settings relative to denitrification. Further research is recommended to improve current understanding on the influence of organic carbon, sulphur and iron electron donors, physical restrictions on microbial activity in dual porosity aquifers, influences of environmental condition (e.g. pH in poorly buffered environments and salinity in coastal or salinized soil settings), co-contaminant influences (particularly the contrasting inhibitory and electron donor influences of pesticides) and improved quantification of denitrification rates in the laboratory and field.     

The influence of elevated levels of sodium in drinking water on elementary and high school students in Massachusetts

Continuing epidemiologic studies at the University of Massachusetts have examined the hypothesis that elevated levels of sodium (Na) in drinking water contribute to elevations of blood pressure (BP). Comparing tenth graders from a town with 107 mg Na/L in the drinking water to those from a town with 8 mg, Na/L, revealed statistically significant and medically important higher BP distributions among the high Na town students relative to their low Na town peers for both systolic and diastolic BP in both boys and girls. The differences were upheld when potentially confounding factors, including dietary Na intake and other water factors occurring differentially in the two water supplies, were controlled in the analysis. A replication study among third graders in the same communities showed similar results.Most recently, an experimental bottled water study assessed the effect on bloodpressure of lowering Na concentration in the water of some of the high sodium community fourth graders. For three months trios of children matched by sex, school, and baseline BP each used different water for all cooking and drinking purposes, with BP monitored bi-weekly. Pupils were randomly allocated to the three water conditions: 1) high sodium water bottled from their own community distribution system, 2) low sodium water bottled from the distribution system of the comparison community with sodium added to the level of the high sodium community water and 3) low sodium water bottled from the distribution system of the low sodium community but with no sodium added.Preliminary results indicate the BP levels of the girls on the low sodium waterexhibited marked decreases in BP over the test period when compared to the other two groups.     

Influence of substrate on fouling in anoxic immersed membrane bioreactors

The influence of carbon substrate chemistry on membrane bioreactor (MBR) fouling in anoxic conditions has been evaluated. The use of a weak carboxylic acid (acetic acid) resulted in the production of large open-floc structures (up to 508microm) that were susceptible to breakage. Primary particles (d(10) and d(20) particle sizes, 5.5+/-1.3 and 15.3+/-8.2microm, respectively) and macromolecular soluble microbial products (SMPs) were generated, directly impacting on membrane fouling. The use of a primary alcohol (ethanol), on the other hand, encouraged the growth of flocs similar to activated sludge. These flocs produced low concentrations of primary particles (d(10) and d(20) particle sizes, 120.6+/-36.1 and 185.2+/-62.7microm, respectively) and high-molecular-weight SMP, and the particles had sufficient mechanical integrity to withstand shear. Consequently, the use of ethanol resulted in sufficient suppression of fouling to extend the filtration time by a factor of three. An increase in MLSS concentration did not directly impact upon fouling when operating with ethanol, primarily because of the low concentration of particulate matter produced.     

Municipal-treated wastewater reuse for plant nurseries irrigation

Results of an experiment aimed at assessing the possibility of reusing reclaimed wastewater for nursery ornamental plants are presented. Tests were carried out in Pistoia (Italy). A pilot plant for tertiary treatment (filtration and peracetic acid + UV disinfection) of the local wastewater treatment plant (WWTP) effluent was set up. An experimental plot with six containerized ornamental species was irrigated with the tertiary effluent and growth and physiological parameters were monitored. A control plot irrigated with fertigated water (nutrient-enriched groundwater) was also set up in order to compare the plants response to different kinds of irrigation water. The refinery treatment by filtration and disinfection with Peracetic Acid (PAA) and UV together was very effective in bacteria removal. The value of 2 MPN of Total Coliforms in 100 ml set by Italian law (until June 2003) for unrestricted irrigation was constantly satisfied. Agronomic results indicate no major limitations to the use of a tertiary effluent as an irrigation source in an ornamental plant nursery. The nutrient content of the tertiary effluent was able to maintain good plant growth as well as fertigated water for most of the tested species.     

Changes in content of microbially available phosphorus,assimilable organic carbon and microbial growth potential during drinking water treatment processes

There are regions where microbial growth in drinking water is limited by phosphorus instead of organic carbon. In phosphorus limited waters small changes in phosphorus concentration significantly affect microbial growth. We studied how water treatment processes in waterworks affect the availability of microbial nutrients and microbial growth potential in drinking water. The nutrients studied were assimilable organic carbon (AOCpotential) and microbially available phosphorus (MAP) which both were quantified by bioassays. Chemical coagulation, commonly used in surfacewater works, effectively removed AOCpotential and MAP. In contrast to activated carbon filtration, ozonation increased the concentrations of AOCpotential and MAP, and also microbial growth potential. In most of the drinking waters, microbial growth was limited by phosphorus, and microbial growth potential correlated with the MAP concentration. Microbial growth potential was lowest in drinking waters produced from surface waters with efficient treatment technique and highest in less treated ground waters.     

硅藻土/纤维素复合助滤剂在微污染原水处理中的应用

以硅藻土和纤维素为原料,通过溶胶-凝胶法制备出了新型硅藻土/纤维素复合助滤剂,探究了各种制备条件对助滤剂的影响,并在高岭土悬浊液中对硅藻土、纤维素和硅藻土/纤维素的助滤性能进行了比较,同时研究了硅藻土/纤维素助滤剂对实际微污染水过滤的影响。研究结果表明:复合助滤剂的最佳制备条件为纤硅比0.67,氨水浓度5.0×10~(-4)mol/L,蒸馏水/纤维素40mL/g,EtOH/硅藻土20mL/g,60℃恒温水浴;硅藻土/纤维素复合助滤剂的助滤性能要明显优于硅藻土和纤维素助滤剂;在微污染原水直接过滤过程中,投加硅藻土/纤维素助滤剂可提高各微污染物的去除率,结合微滤膜深度处理工艺,最终出水水质满足《生活饮用水卫生标准》(GB 5749—2006)的要求。     

A quantitative measure of nitrifying bacterial growth

Nitrifying bacteria convert ammonia (NH3) to nitrate (NO3-) in a nitrification reaction. Methods to quantitatively separate the growth rate of these important bacterial populations from that of the dominant heterotrophic bacteria are important to our understanding of the nitrification process. The changing concentration of ammonia is often used as an indirect measure of nitrification but ammonification processes generate ammonia and confound this approach while heterotrophs remove nitrate via denitrification. Molecular probe methods can tell us what proportion of the microbial community is nitrifying bacteria but not their growth rate. The technique proposed here was able to quantify the growth rate of the nitrifying bacterial populations amidst complex ecological processes. The method incubates [methyl-3H] thymidine with water samples in the presence and absence of an inhibitor of nitrification-thiourea. The radioactively labeled DNA in the growing bacteria was extracted. The rate of incorporation of the label into the dividing bacterial DNA was used to determine bacterial growth rate. Total bacterial community growth rates in full-scale and pilot-scale fixed-film nitrifying reactors and an activated sludge reactor were 2.1 x 10(8), 4.1 x 10(8) and 0.4 x 10(8)cell ml(-1)d(-1), respectively; the growth rate of autotrophic-nitrifying bacteria was 0.7 x 10(8), 2.6 x 10(8) and 0.01 x 10(8)cell ml(-1)d(-1), respectively. Autotrophic-nitrifying bacteria contributed 30% and 60% of the total bacterial community growth rate in the nitrifying reactors whereas only 2% was observed in the activated sludge reactor that was not designed to nitrify. The rates of ammonia loss from the nitrifying reactors corresponded to the rate of growth of the nitrifying bacteria. This method has the potential to more often identify factors that enhance or limit nitrifying processes in both engineered and natural aquatic environments.