Ken J. Hall

Biochemical model for enhanced biological phosphorus removal

Abstract Enhanced biological phosphorus (bio-P) removal from wastewater is a promising technology for which the fundamental mechanisms are still unclear. The purpose of this paper is to present a biochemical model that explains bio-P removal mechanisms occurring under anaerobic, aerobic and anoxic conditions of the process. A bio-P bacterium is referred to as one that can store both polyphosphate and carbon (as poly-β-hydroxybutyrate for example). In this communication, observations from the literature are first reviewed and mechanisms of bacterial bioenergetics and membrane transport are summarized. The model for bio-P metabolism under anaerobic, aerobic and anoxic conditions is then presented. The role of polyphosphate under anaerobic conditions is suggested to be as a source of energy both for the reestablishment of the proton motive force, which would be consumed by substrate transport and for substrate storage. The role of the anaerobic zone is to maximize the storage of organic substrates in bio-P bacteria. For this purpose the supply of readily available substrates should be maximized and the presence of electron acceptors (molecular oxygen or oxidized nitrogen) minimized. Under subsequent aerobic or anoxic conditions, bio-P bacteria will accumulate polyphosphates in response to the availability of electron acceptors (oxygen or oxidized nitrogen) for energy production. Carbon reserves in bio-P bacteria should provide energy for growth and for soluble phosphate accumulation as polyphosphate reserves.

Sources, pathways, and relative risks of contaminants in surface water and groundwater: a perspective prepared for the Walkerton inquiry.

On a global scale, pathogenic contamination of drinking water poses the most significant health risk to humans, and there have been countless numbers of disease outbreaks and poisonings throughout history resulting from exposure to untreated or poorly treated drinking water. However, significant risks to human health may also result from exposure to nonpathogenic, toxic contaminants that are often globally ubiquitous in waters from which drinking water is derived. With this latter point in mind, the objective of this commission paper is to discuss the primary sources of toxic contaminants in surface waters and groundwater, the pathways through which they move in aquatic environments, factors that affect their concentration and structure along the many transport flow paths, and the relative risks that these contaminants pose to human and environmental health. In assessing the relative risk of toxic contaminants in drinking water to humans, we have organized our discussion to follow the classical risk assessment paradigm, with emphasis placed on risk characterization. In doing so, we have focused predominantly on toxic contaminants that have had a demonstrated or potential effect on human health via exposure through drinking water. In the risk assessment process, understanding the sources and pathways for contaminants in the environment is a crucial step in addressing (and reducing) uncertainty associated with estimating the likelihood of exposure to contaminants in drinking water. More importantly, understanding the sources and pathways of contaminants strengthens our ability to quantify effects through accurate measurement and testing, or to predict the likelihood of effects based on empirical models. Understanding the sources, fate, and concentrations of chemicals in water, in conjunction with assessment of effects, not only forms the basis of risk characterization, but also provides critical information required to render decisions regarding regulatory initiatives, remediation, monitoring, and management. Our discussion is divided into two primary themes. First we discuss the major sources of contaminants from anthropogenic activities to aquatic surface and groundwater and the pathways along which these contaminants move to become incorporated into drinking water supplies. Second, we assess the health significance of the contaminants reported and identify uncertainties associated with exposures and potential effects. Loading of contaminants to surface waters, groundwater, sediments, and drinking water occurs via two primary routes: (1) point-source pollution and (2) non-point-source pollution. Point-source pollution originates from discrete sources whose inputs into aquatic systems can often be defined in a spatially explicit manner. Examples of point-source pollution include industrial effluents (pulp and paper mills, steel plants, food processing plants), municipal sewage treatment plants and combined sewage-storm-water overflows, resource extraction (mining), and land disposal sites (landfill sites, industrial impoundments). Non-point-source pollution, in contrast, originates from poorly defined, diffuse sources that typically occur over broad geographical scales. Examples of non-point-source pollution include agricultural runoff (pesticides, pathogens, and fertilizers), storm-water and urban runoff, and atmospheric deposition (wet and dry deposition of persistent organic pollutants such as polychlorinated biphenyls [PCBs] and mercury). Within each source, we identify the most important contaminants that have either been demonstrated to pose significant risks to human health and/or aquatic ecosystem integrity, or which are suspected of posing such risks. Examples include nutrients, metals, pesticides, persistent organic pollutants (POPs), chlorination by-products, and pharmaceuticals. Due to the significant number of toxic contaminants in the environment, we have necessarily restricted our discussion to those chemicals that pose risks to human health via exposure through drinking water. A comprehensive and judicious consideration of the full range of contaminants that occur in surface waters, sediments, and drinking water would be a large undertaking and clearly beyond the scope of this article. However, where available, we have provided references to relevant literature to assist the reader in undertaking a detailed investigation of their own. The information collected on specific chemicals within major contaminant classes was used to determine their relative risk using the hazard quotient (HQ) approach. Hazard quotients are the most widely used method of assessing risk in which the exposure concentration of a stressor, either measured or estimated, is compared to an effect concentration (e.g., no-observed-effect concentration or NOEC). A key goal of this assessment was to develop a perspective on the relative risks associated with toxic contaminants that occur in drinking water. Data used in this assessment were collected from literature sources and from the Drinking Water Surveillance Program (DWSP) of Ontario. For many common contaminants, there was insufficient environmental exposure (concentration) information in Ontario drinking water and groundwater. Hence, our assessment was limited to specific compounds within major contaminant classes including metals, disinfection by-products, pesticides, and nitrates. For each contaminant, the HQ was estimated by expressing the maximum concentration recorded in drinking water as a function of the water quality guideline for that compound. There are limitations to using the hazard quotient approach of risk characterization. For example, HQs frequently make use of worst-case data and are thus designed to be protective of almost all possible situations that may occur. However, reduction of the probability of a type II error (false negative) through the use of very conservative application factors and assumptions can lead to the implementation of expensive measures of mitigation for stressors that may pose little threat to humans or the environment. It is important to realize that our goal was not to conduct a comprehensive, in-depth assessment of risk for each chemical; more comprehensive assessments of managing risks associated with drinking water are addressed in a separate issue paper by Krewski et al. (2001a). Rather, our goal was to provide the reader with an indication of the relative risk of major contaminant classes as a basis for understanding the risks associated with the myriad forms of toxic pollutants in aquatic systems and drinking water. For most compounds, the estimated HQs were < 1. This indicates that there is little risk associated with exposure from drinking water to the compounds tested. There were some exceptions. For example, nitrates were found to commonly yield HQ values well above 1 in- many rural areas. Further, lead, total trihalomethanes, and trichloroacetic acid yielded HQs > 1 in some treated distribution waters (water distributed to households). These latter compounds were further assessed using a probabilistic approach; these assessments indicated that the maximum allowable concentrations (MAC) or interim MACs for the respective compounds were exceeded <5% of the time. In other words, the probability of finding these compounds in drinking water at levels that pose risk to humans through ingestion of drinking water is low. Our review has been carried out in accordance with the conventional principles of risk assessment. Application of the risk assessment paradigm requires rigorous data on both exposure and toxicity in order to adequately characterize potential risks of contaminants to human health and ecological integrity. Weakness rendered by poor data, or lack of data, in either the exposure or effects stages of the risk assessment process significantly reduces the confidence that can be placed in the overall risk assessment. (ABSTRACT TRUNCATED)

DYNAMICS OF CARBON RESERVES IN BIOLOGICAL DEPHOSPHATATION OF WASTEWATER

ABSTRACT A series of batch tests were conducted to investigate the effects of short chain fatty acids (SCFAs) on carbon storage and consumption involved in the biological dephosphatation of wastewater. Nitrate and nitrite were tested as alternatives to oxygen to assess the importance of denitrifying microorganisms in the phosphorus removal process. Both poly-β-hydroxybutyrate (PHB) and poly-β-hydroxyvalerate (PHV) were stored as carbon reserve material under anaerobic conditions, and consumed under aerobic conditions. The proportion of carbon storage as PHB was larger than that as PHV with the addition of SCFAs containing an even number of carbons (acetate, butyrate), whereas the proportion of PHV was larger when SCFAs with an odd number of carbons were added (propionate, lactate, valerate). Maximum PHV accumulation was reported with combined acetate and propionate addition. With the dephosphating sludge studied, acetate and propionate were the two most “readily stored” carbon substrates. Under aerobic conditions, phosphate uptake, PHB and PHV consumption were reported. Nitrate, but not nitrite, was found to have a similar effect to oxygen. A classification of microbial activity in a dephosphating biomass was presented. It was proposed that PHA storage plays a central role in biological dephosphatation and that the function of the anaerobic zone is to maximize carbon storage in dephosphating bacteria in order to subsequently maximize phosphate uptake under aerobic conditions.

Molecular size and spectral characterization of organic matter in a meromictic lake

Abstract Gel filtration has been used to investigate the properties of natural organic matter in the aquatic environment. The organic compounds in colored lake water, fallen leaves and surface sediment extracts were separated into molecular size fractions which varied from larger than 50,000 to less than 700 when compared to dextrans. These fractions had different color and fluorescence properties. Spectral analysis (i.r., u.v., and fluorescence) provided evidence that fractions from Sephadex columns were fragments of a system of polymers with slightly different chemical characteristics. Degradation of the organic concentrates and molecular size fractions from Sephadex columns by alkline—CuO oxidation and sodium-amalgam reduction techniques permitted six “chemical subunits”, namely dibutyl phthalate, vanillin, catechol, 4-hydroxyacetophenone, 3,5-dihydroxybenzoic acid and resorcinol to be identified using thin layer chromatography and infrared spectroscopy.

A preliminary model for predicting heavy metal contaminant loading from an urban catchment.

The toxicity of heavy metals to biota in urban catchments has been regarded as a very important non-point source pollution issue. Numerous studies on heavy metal pollution in urban receiving waters have found that metal transport by surface runoff is closely correlated to the partitioning of the metal forms between dissolved and particulate phases, where sediment plays an important role in the transport process. Sediment cycling on urban streets, metal binding form, and rainfall character in the catchment area are considered to be the key factors for metal transport. A preliminary model is developed based on these considerations. Starting from classical build-up and wash-off processes for the suspended sediment (SS) on the urban impervious surface, the model links the transport of suspended sediment to the transport of metal species. Monitoring data from a small highway catchment were used in the model development. A total of 47 rain events over 1 year were monitored intensively at short time intervals (5-10 min) for hydrological data, rainfall intensity, and stormwater quality. In developing the model, lead was used for the metal load prediction, as it has been a common fuel additive for urban transportation. Agreement between model results and monitoring data indicates that the model can be used in predicting metal load from impervious urban areas, such as streets and roadways, on a long-term basis.

Limnological contrasts and anomalies in two adjacent saline lakes

Differences in physical, chemical, and biological conditions in two small (<20 ha) saline lakes less than 1 km apart in south-central British Columbia are examined. Although the lake basins are morphometrically similar, differences in their watershed geology and topography in large part may be responsible for the more saline lake showing severe and anomalous meromictic features while the less saline lake exhibits normal dimictic characteristics. Bacterial and phytoplankton population densities and production profiles of the lakes are compared along with some aspects of their zooplankton populations.

Sludge digestion using ORP-regulated aerobic-anoxic cycles

Abstract This work documents the results from two lab-scale reactors digesting waste sludge in an aerobic-anoxic fashion. The control reactor “fixed” the length of the aerobic-anoxic cycle at 6 h, with each segment of the cycle set at 3 h each. The experimental reactor used ORP to control the total length of the cycle based upon the distinctive “nitrate breakpoint” occurring in the ORP-time profile. The reactors were evaluated on the basis of removals for TSS, VSS, nitrogen and phosphorus. In addition, the control stability achieved when the reactors were subjected to spikes of specific chemicals was monitored. The ORP-regulated reactor better accommodated the disturbances, as well as appeared to show an increase in the removal of nitrogen and solids.

Fossil carotenoids and paleolimnology of meromictic Mahoney Lake, British Columbia, Canada

Vertical distribution of fossil carotenoids in a sediment core from meromictic Mahoney Lake was studied. Besides okenone and demethylated okenone, lutein and zeaxanthin andβ-carotene isomers were identified. No carotenoids typical for purple nonsulfur or green sulfur bacteria were detected. The ratio of zeaxanthin to lutein (above 1:1 in all samples) indicates a dominance of cyanobacteria over green algae in the phytoplankton assemblages of the past. Okenone, which is found exclusively in Chromatiaceae, was the dominating carotenoid in all sediment zones.The oldest sediment layers containing okenone were deposited 11 000 years ago. Between 9000 and 7000 and since 3000 years b.p., Chromatiaceae reached a considerable biomass in the lake. Vertical changes in okenone concentration were not related to changes of paleotemperatures. In contrast, okenone concentrations decreased during periods of volcanic ash input. During most of the lake history, however, mean okenone concentrations were positively correlated with sedimentation rates. This indicates that vertical changes of okenone concentration in the sediment reflect past changes of purple sulfur bacterial biomass in the lake.According to these results, the past limnology of Mahoney Lake resembled that of the present with a sulfide-containing monimolimnion and a well-developed population of okenone-bearing purple sulfur bacteria.

Diversity, distribution and physiology of the aerobic phototrophic bacteria in the mixolimnion of a meromictic lake

The population of anoxygenic phototrophic bacteria in the aerobic zone of the meromictic Mahoney Lake was investigated using classical microbiological methods. This bacterial community was found to be very rich and diverse. Thirty-one new strains of the obligately aerobic phototrophic bacteria, and two new purple nonsulfur strains, were isolated in pure cultures and preliminarily characterized. The isolates contain a variety of carotenoids, bacteriochlorophyll a incorporated into pigment protein complexes, and are morphologically and physiologically diverse. These properties indicate a diversity of adaptations to the stratified environments of this meromictic lake. Phylogenetically all isolated strains belong to the alpha subclass of Proteobacteria.

Midge-and diatom-based palaeosalinity reconstructions for Mahoney Lake, Okanagan Valley, British Columbia, Canada

Salinity fluctuations in lakes of semi-arid regions have long been recognised as indicators of palaeoclimatic change, and have provided a valuable line of evidence in palaeo-climatic reconstruction. In the present study, fossil remains of diatoms and midges were used to reconstruct salinity changes at Mahoney Lake from the early postglacial, through the early, mid and late Holocene. A transition from midges typical of a freshwater community (Protanypus, Sergentia, Heterotrissocladius, Cladopelma, Dicrotendipes) during the early postglacial, to those indicative of saline environments (Cricotopus/Orthocladius, Tanypus) occurred in the early Holocene. The midge-inferred salinity values reflected the shift from freshwater (0.031 g/L) immediately after deglaciation, to saline water (2.4 to 55.2 g/L) in subsequent periods. A less saline period was found to have occurred after 1000 yr BP, suggesting a cooler or wetter period. The diatom record indicates similar trends, with freshwater taxa (e.g.,Cyclotella bodanica var. aff.lemanica) dominating near the bottom of the core. Diatom-inferred salinities indicate that saline conditions (about 30 g/L) prevailed throughout subsequent Holocene time, although relatively fresh conditions are indicated following deposition of the Mazama Ash, and from about 1500 yr BP until the present day. Midge and diatom-inferred salinity reconstructions for Mahoney Lake compare favorably with each other, and with climate trends inferred from earlier palynological evidence. The palaeosalinity record thus contributes new data relevant to past climatic conditions, in a region where little data have previously been collected.