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Water safety plans address both routine operations and incident responses to support risk management in drinking water utilities. Their use and relevance in facing the challenges of the Covid-19 crisis were investigated via a survey distributed to water utilities and health or environmental agencies across the globe. Responses from 86 respondents from 38 countries were analysed to identify the water safety challenges faced and responses. Water safety plans appear to provide some preparedness and organizational advantages to utilities in facing the Covid-19 crisis, including stronger communication links between utilities and governing agencies. Guidance for future water safety planning is provided. [ABSTRACT FROM AUTHOR]

Quantitative microbial risk assessment (QMRA), the assessment of microbial risks when model inputs and estimated health impacts are explicitly quantified, is a valuable tool to support water safety plans (WSP). In this paper, research studies undertaken on the application of QMRA in drinking water systems were reviewed, highlighting their relevance for WSP. The important elements for practical implementation include: the data requirements to achieve sufficient certainty to support decision-making; level of expertise necessary to undertake the required analysis; and the accessibility of tools to support wider implementation, hence these aspects were the focus of the review. Recommendations to support the continued and growing application of QMRA to support risk management in the water sector are provided. [ABSTRACT FROM AUTHOR]

This study employed Quantitative Microbial Risk Assessment (QMRA) to estimate the gastrointestinal risks associated with Cryptosporidium and Giardia discharged from three STPs located within the Lake Burragorang catchment. The QMRA considered baseline and various hazardous event scenarios (e.g. plant failure and heavy rainfall). Under baseline conditions, the combined effect of constructed barriers, catchment barriers and dilution reduced pathogen numbers from the discharge of all three STPs by 10 to 14 orders of magnitude. This was sufficient for the risk to be well below currently mooted benchmarks of 'tolerable risk', even when relatively conservative assumptions were applied. For all hazardous event scenarios, the level of risk remained low, which illustrated the benefit of multiple barriers. Provisionally it appears that the STPs currently discharging into the waterways of the catchment do not pose an unacceptable or unmanageable risk to Sydney's drinking water consumers. [ABSTRACT FROM AUTHOR]

Some national drinking water guidelines provide guidance on how to define 'safe' drinking water. Regarding microbial water quality, a common position is that the chance of an individual becoming infected by some reference waterborne pathogen (e.g. Cryptsporidium) present in the drinking water should <10-4 in any year. However the instantaneous levels of risk to a water consumer vary over the course of a year, and waterborne disease outbreaks have been associated with shorter-duration periods of heightened risk. Performing probabilistic microbial risk assessments is becoming commonplace to capture the impacts of temporal variability on overall infection risk levels. A case is presented here for adoption of a shorter-duration reference period (i.e. daily) infection probability target over which to assess, report and benchmark such risks. A daily infection probability benchmark may provide added incentive and guidance for exercising control over short-term adverse risk fluctuation events and their causes. Management planning could involve outlining measures so that the daily target is met under a variety of pre-identified event scenarios. Other benefits of a daily target could include providing a platform for managers to design and assess management initiatives, as well as simplifying the technical components of the risk assessment process. [ABSTRACT FROM AUTHOR]

A hierarchical Bayesian framework was applied for describing variability in pathogen concentration (with associated uncertainty) from presence/absence observations for E. coli O157:H7. Laboratory spiking experiments (method performance) and environmental sample assays were undertaken for a surface drinking water source in France. The concentration estimates were strongly dependent upon the assumed statistical model used (gamma, log-gamma or log-gamma constrained), highlighting the need for a solid theoretical basis for model choice. Bayesian methods facilitate the incorporation of additional data into the statistical analysis; this was illustrated using faecal indicator results of E. coli (Colilert®) to reduce the posterior parameter uncertainty and improve model stability. While conceptually simple, application of these methods is still specialised, hence there is a need for the development of data analysis tools to make Bayesian simulation techniques more accessible for QMRA practitioners. [ABSTRACT FROM AUTHOR]

Pathogenic microorganisms have been identified as the main human health risks associated with the reuse of treated urban stormwater (runoff from paved and unpaved urban areas). As part of the Smart Water initiative (Victorian Government, Australia), a collaborative evaluation of three existing integrated stormwater recycling systems, and the risks involved in non-potable reuse of treated urban stormwater is being undertaken. Three stormwater recycling systems were selected at urban locations to provide a range of barriers including biofiltration, storage tanks, UV disinfection, a constructed wetland, and retention ponds. Recycled water from each of the systems is used for open space irrigation. In order to adequately undertake exposure assessments, it was necessary to quantify the efficacy of key barriers in each exposure pathway. Given that none of the selected treatment systems had previously been evaluated for their treatment efficiency, experimental work was carried out comprising dry and wet weather monitoring of each system (for a period of 12 months), as well as challenging the barriers with model microbes (for viruses, bacteria and parasitic protozoa) to provide input data for use in Quantitative Microbial Risk Assessment. [ABSTRACT FROM AUTHOR]

Waterborne disease outbreaks have been associated with periods of heightened source water pathogen concentrations in treated drinking-water supplies. For their management it is necessary to identify and quantify the impacts of events which lead to adverse concentration fluctuations. The aim of this work was to estimate relative microbial risks to water consumers arising from one such event: rainfall-induced runoff entering a surface drinking-water reservoir in an Australian agricultural catchment. Runoff events are known to influence both the source water entering a reservoir and the ability of a reservoir to act as a barrier to pathogen progression. Hydrograph separation methods were used to distinguish 'runoff event' from baseflow periods and pathogen concentrations of the inflow to the reservoir during runoff and baseflow periods respectively were estimated. Relative impacts of runoff event periods on health risks to consumers were assessed using Quantitative Microbial Risk Assessment principles. Runoff event conditions predominated 14% of the time. The proportions of infections attributable to runoff event periods from Cryptosporidium, Giardia and Campylobacter spp. were 57 %, 80 %, and 28% respectively. Daily infection risks were greatest in winter months than other seasons primarily due to the higher frequency of runoff events. Results from this and similar analyses, aiming to assess impacts of explicitly identified events on consumer health risks, provides important information for water system risk management, e.g. identifying periods of heightened risk and setting management priorities. [ABSTRACT FROM AUTHOR]

An approach to aid decision making for urban water management is presented that is based on the concept of trade-off sacrifice level in pairwise comparisons between criteria, modelled using fuzzy logic. This approach is illustrated by a case study -- selection of alternative water supplies for a Sydney household. Four key decision making criteria covering health, economic, environment and technical aspects are selected: annual probability of infection, life cycle energy use, life cycle cost and reliability. The decision making problem is to select between cases with different volume and application of recycled greywater and rainwater in light of the four criteria. Decision maker's preference is expressed by five levels of trade-off sacrifice between pairs of criteria. The decision makers can assign their preferences for sacrifice level by linguistic assessment and the output trade-off weight (TOW). Measures of decision makers' perceived trade-off level are modelled by a rule-based fuzzy logic control system. The final analysis shows the performance for each sacrifice class for each case, to aid overall decision making with stakeholders. [ABSTRACT FROM AUTHOR]

Risk mitigation provided by human monitoring and control over a water supply system has been consistently overlooked when estimating pathogen exposure to consumers. The Systems-Actions-Management (SAM) framework lends itself neatly to Quantitative Microbial Risk Assessment (QMRA) as one way to establish this link. The general premise is that an organisational protocol will influence how a human controller behaves, in turn influencing the system performance. For illustrative purposes, the framework was applied to a hypothetical water supply system to quantify the risk reduction offered by routine Cryptosporidium monitoring and the response to oocyst ‘detects’. Our findings suggest that infrequent direct pathogen monitoring may provide a negligible risk barrier. The practice of sampling treated water to verify microbiological integrity is also dubious: oocyst densities were largely under-estimated, in part due to the spatial dispersion of oocysts in the waterbody, but predominantly from imperfect detection methods. The development of ‘event-driven’ monitoring schemes with barrier performance-based treatment verification methods, as promoted in new guidelines, is supported as a pressing issue to reduce the likelihood of undetected pathogen passage through a treatment plant. [ABSTRACT FROM AUTHOR]

In this paper the results of a sampling programme, undertaken as part of the EU MicroRisk project, are described. This project was undertaken to ascertain the occurrence of pathogens and indicators in the River Thames and their subsequent removal through a treatment works. Appropriate physico-chemical surrogates, as determined by statistical correlation are proposed for the microorganisms identified in the raw water. This study shows that under normal raw water conditions the treatment works is able to remove microbial contamination with a significant margin of safety. [ABSTRACT FROM AUTHOR]

New WHO and Australian guidelines promote a risk-management approach for minimising exposure to pathogens in recreational waters. Between 2003 and 2005, they were applied to Lake Parramatta (10 ha, 450 ML), a potential recreation site in Sydney, Australia. A three stage approach was developed involving (1) initial suitability assessment using historic data, (2) revised suitability assessment based on new data and (3) characterisation of hazardous (especially wet weather) events. Contrary to the stage 1 suitability classification, stage 2 baseline data indicated that during dry weather the lake had water quality sufficient for primary contact recreation (95th percentiles for enterococci = 19 MPN/100, n = 50) and the major pathogen source was wildfowl. Guideline principles provided a rationale for collecting microbiological and geographic data needed to understand local cycles of lake contamination/recovery. The concept of hazardous events was particularly useful. Studies of stormwater events led us to identify a transition point (>10 mm rainfall in 24 h) where human-faecal pathogen risks increased and access needed to be controlled. Together baseline and event data yielded operational tools (i.e. event detection methods, action triggers, auditing criteria, remediation priorities) for minimising bather exposure. [ABSTRACT FROM AUTHOR]

Concentrations of microbiological contaminants in streams increase during rainfall-induced higher flow 'event' periods as compared to 'baseflow' conditions. If the stream feeds a drinking water reservoir, such periods of heightened pathogen loads may pose a challenge to the water treatment plant and subsequently a health concern to water consumers downstream. In order to manage this risk, it is desirable to first quantify the differences in surface water quality between baseflow and event conditions. The Event Mean Concentration (EMC) is a flow-weighted average concentration of a contaminant over the duration of a single event, proposed here as a standard parameter for quantifying the net effect of events on microbial water quality. Application of the EMC concept was assessed using flow and quality data for several events from an urbanised catchment. Expected mean EMCs were significantly larger than expected mean baseflow concentrations (p-value≤0.012) for three microbial agents - Escherichia coli (13,000 [n = 7] v. 610 [n = 16] mpn/100 ml), Cryptosporidium (234 [n = 6] v. 51 [n = 16] oocysts/10 litres) and Campylobacter (48 [n = 5] v. 2.1 [n = 16] mpn/100 ml). These parameter estimates were complemented by estimating data variability and uncertainty in the form of second-order random variables. As such the results are in a format appropriate for potential use as components in probabilistic risk assessments evaluating the effect runoff events have on drinking water quality. [ABSTRACT FROM AUTHOR]

There is uncertainty whether Cryptosporidium oocysts attach to particles or to each other under ambient water conditions. Particle size distributions of Cryptosporidium oocyst suspensions were determined over a range of ionic strengths and pHs to determine under those environmental conditions that may promote oocyst aggregation. Cryptosporidium oocysts were shown to only aggregate in high ionic strength solutions (> 0.45 M) and remain largely as single entities at ionic strengths and pHs that were likely to be encountered in surface runoff. Similarly, in loam soil suspensions, rather than attaching to the soil particles the majority of oocysts also remained as single entities. Overall, oocysts are expected to remain largely unattached to either themselves or soil particles in overland runoff. This has implications for pathogen transport and modelling since oocysts that are freely suspended are more likely to be transported in runoff to surface waters than if attached to more dense soil/faecal particles. [ABSTRACT FROM AUTHOR]

Distribution pipe biofilms can provide sites for the concentration of a wide range of microbial pathogens, thereby acting as a potential source of continual microbial exposure and furthermore can affect the aesthetic quality of water. In a joint project between Stockholm Water, the MISTRA "Sustainable Urban Water" program, the Swedish Institute for Infectious Disease Control and the Royal Technical University, Stockholm, the aim of the current study was to investigate biofilms formed in an urban water distribution system, and quantify the impact of such biofilms on potential pathogen accumulation and persistence within the Greater Stockholm Area, Sweden. When used for primary disinfection, ultra-violet (UV) treatment had no measurable influence on biofilm formation within the distribution system when compared to conventional chlorination. Biofilms produced within a model pilot-plant were found to be representative to those that had formed within the larger municipal water distribution system, demonstrating the applicability of the novel pilot-plant for future studies. Polystyrene microspheres (1.0 µm) and Salmonella bacteriophages demonstrated their ability to accumulate and persist within the model pilot-plant system, where the means of primary disinfection (UV-treatment, chlorination) had no influence on such phenomena. With the exception of aeromonads, potential pathogens and faecal indicators could not be detected within biofilms from the Stockholm water distribution system. Results from this investigation may provide information for water treatment and distribution management strategies, and fill key data gaps that presently hinder the refinement of microbial risk models. [ABSTRACT FROM AUTHOR]

This paper describes the development and testing of a mathematical model as a tool to quantify pathogen loads in Sydney's drinking water catchments. It has been used to identify, quantify and prioritise sources of Cryptosporidium, Giardia and E. coli in the Wingecarribee catchment. The pathogen model promotes understanding of the relative significance of different sources of pathogen risks as well as their fate and transport as they move through the subcatchments. This pathogen model not only enables water utility managers to identify those catchment segments that may contribute the highest load of pathogens, but also where management options will be most effective. [ABSTRACT FROM AUTHOR]

The quality of effluent from an on-site sewage treatment system is a critical factor in designing the disposal area and, hence, ensuring the sustained performance of the system. Contaminant concentrations in effluent are typically specified in regulatory guidelines or standards; however, the accuracy of these guideline values are brought into question due to the poor performance of septic tanks and the high failure rates of disposal systems reported here and elsewhere. Results from studies of septic tank effluent quality indicated that the effluent is of poorer quality than currently suggested by guidelines. Aerated wastewater treatment systems were found to perform to accreditation guidelines; however, insufficient nutrient data is presently available to assess nutrient loads. It is proposed that the 80th percentile of system performance be adopted as the design value for sizing effluent disposal areas to minimise failure associated with overloading. For septic tanks this equates to 660 mg L-1>>>> SS, 330 mg L-1>>>> BOD, 250 mg L-1>>>> TN and 36 mg L-1>>>> TP. [ABSTRACT FROM AUTHOR]

Hazard Analysis and Critical Control Points (HACCP) was applied for identifying and controlling exposure to pathogenic microorganisms encountered during normal sludge and wastewater handling at a 12,500 m³/d treatment plant utilising tertiary wastewater treatment and mesophilic sludge digestion. The hazardous scenarios considered were human exposure during treatment, handling, soil application and crop consumption, and exposure via water at the wetland-area and recreational swimming. A quantitative microbial risk assessment (QMRA), including rotavirus, adenovirus, haemorrhagic E. coli, Salmonella, Giardia and Cryptosporidium, was performed in order to prioritise pathogen hazards for control purposes. Human exposures were treated as individual risks but also related to the endemic situation in the general population. The highest individual health risk from a single exposure was via aerosols for workers at the belt press for sludge dewatering (virus infection risk = 1). The largest impact on the community would arise if children ingested sludge at the unprotected storage site, although in the worst-case situation the largest number of infections would arise through vegetables fertilised with sludge and eaten raw (not allowed in Sweden). Acceptable risk for various hazardous scenarios, treatment and/or reuse strategies could be tested in the model. [ABSTRACT FROM AUTHOR]

A simplistic quantitative microbial risk assessment (QMRA) based on the maximum risk curve (r = 1) was developed for Legionella within a water distribution system. Both biofilms and a thermophilic isolate of acanthamoebae were shown to increase the resistance of Legionella to conventional thermal disinfection by between one and two logs respectively. The level of risk presented to consumers was shown to exceed the USEPA 10-4 benchmark in many cases tested. This was caused, in part, by the sensitivity of the risk model but also through a lack of reliable dose-response data for Legionella. Notwithstanding this, the current study provided comparative information on the efficacy of conventional disinfection against Legionella. Combined chlorine was shown to reduce the risk of infection by as much as 1-log when compared to free chlorine, although thermal disinfection provided the most effective means of risk reduction. Biofilm detachment and the interaction of Legionella with acanthamoebae were two important ecological factors that significantly increased the risk of legionellosis, and thus should be further considered in the refinement of QMRA models. [ABSTRACT FROM AUTHOR]

The supply of unfiltered disinfected drinking water from Melbourne's fully protected catchments means that the water-quality managers must ensure that the source water poses no public health risk. High turbidity is currently used as a surrogate of pathogens, and harvesting of water is based on its measurement. The work presented here summarises suspended particle and associated pathogen, microbial indicator and faecal biomarker concentrations collected to (a) quantify turbidity in an Australian water supply system and (b) assess the possibility of increasing water harvesting from selected tributaries. Pathogens and microbial indicators were present in low numbers in these source waters; increased turbidity during storm events was not associated with an increase in pathogen concentration. The results confirmed that protected catchments, along with good management, were effective barriers to pathogen contamination. Aesthetic issues still need to be addressed, but no measurable increase in microbiological risk was associated with storm-generated particles. [ABSTRACT FROM AUTHOR]

Distribution pipe biofilms present a currently unquantified public health risk to consumers receiving water for domestic potable and non-potable use. The aim of this study was to quantify the numbers of legionellae, used here as model bacterial pathogens, that may accumulate, persist within and detach from distribution pipe biofilms. L. pneumophila recovered by standard culture from an 8 week-old biofilm formed within a novel pilot-scale water distribution system represented 1% of those present in the adjacent bulk water. A combined chlorine concentration exceeding 0.2 mg.L-1 eliminated culturable sessile legionellae altogether, though the reduction in FISH-positive cells represented just 75 ± 25% of the original amount, compared to a 5-log reduction in culturable cells during the same period. Where there was < 0.1 mg.L-1 combined chlorine, an exponential decay/loss of sessile L. pneumophila was observed (k = 0.37 - 0.41) over the course of a 38-day experimental period. The inoculation of the system with 1 µm fluorescent microspheres and legionellae demonstrated that removal of the latter was dominated by chemical disinfection, with erosion and biological grazing playing lesser roles. Under turbulent (Re ∼ 5000) conditions, larger clusters of biofilm become detached from substrata, with more than 90% of sessile legionellae mobilised into the bulk water phase. Interaction with both biofilms and a thermophilic Acanthamoeba isolate reduced the susceptibility of legionellae to thermal inactivation by between one and two orders of magnitude, though it increased their sensitivity to chemical (free and combined chlorine) disinfection. [ABSTRACT FROM AUTHOR]

Through their many sorption sites, microbial biofilms can accumulate both organic and inorganic particulate and colloidal material from bulk water environments. An application of such first principles to the ecology of "biocolloidal" enteric virions would suggest that they too may be concentrated by biofilms in a similar way. Though previous studies have isolated human gastrointestinal (enteric) virions from microbial biofilms, the exact human health significance of this has been neither fully investigated nor completely understood. Through an assessment of the location, accumulation and persistence of model enteric virions (øX174, MS2 and B40-8 bacteriophages as well as 20 nm fluorescent latex microspheres) within biofilms, the aim of the current study was to investigate whether the interaction of enteric virions with distribution pipe biofilms could provide a secondary source of public health concern to consumers. Model enteric virions were found to be incorporated into biofilms at concentrations representing 1% of those present in the adjacent bulk water environment. A sub-population (0.01%) of these persisted throughout an experimental period of 30 days, inferring their potential to accumulate over time. Furthermore, model enteric virions were partitioned into bacterial microcolonies, environments where biofilm bacteria can persist and re-grow, even in the presence of "acceptable" levels of disinfection. A risk model for enteric virion accumulation and release from distribution pipe biofilms suggested that associated risks may exceed USEPA benchmark values. These findings could have wide-reaching implications in water treatment and distribution strategies, and necessitate a re-appraisal of current water guideline values. [ABSTRACT FROM AUTHOR]

A consortium with autotrophic anaerobic ammonium oxidising (AAAO) activity was developed from municipal sludge, and its ability to remove high ammonium concentrations in a toxic wastewater such as coke ovens wastewater is presented here. The enriched AAAO consortium was acclimatised to a synthetic coke ovens wastewater to establish anaerobic ammonium oxidation (AAO) activity. Phenol was the main carbon component of the synthetic wastewater whereby it was added stepwise from 50±10 to 550±10 mg l–1 into an anammox enrichment medium. Ammonium-N removal was initially impaired; however, it gradually recovered. After 15 months of further selection and enrichment, the ammonium removal rate reached 62±2 mg NH4+-N l–1 day–1, i.e. 1.5 times the rate in the original AAAO reactor. The new consortium demonstrated higher ammonium and nitrite removal rates, even under phenol perturbation (up to 330±10 mg l–1). It is therefore concluded that the AAO activity in the consortium was resistant to high phenol and has potential for treating coke-ovens wastewater. [ABSTRACT FROM AUTHOR]

The option for biological nitrogen removal has recently been broadened with the description of simultaneous nitrification/denitrification, anaerobic ammonium oxidation (ANAMMOX) and the concept of CANON (completely autotrophic nitrogen removal over nitrite). An autotrophic anaerobic ammonium oxidation (AAAO) consortium was successfully selected and enriched from municipal treatment plant sludges in Sydney, Australia, but not from industrial coke-oven wastewater sludges. Chemolithoautotrophic basic salt (CLABS) medium was used in the selection of AAAO organisms and chloramphenicol was added to the initial stage of selection to eliminate denitrifiers. Two different temperatures, 37°C and 55°C, were used in the selection of mesophilic and thermophilic consortia, respectively. Thermophilic AAAO organisms were not selected at 55°C. Mesophilic AAAO activities, however, were evident in both batch and continuous cultures, whereby ammonium was consumed concurrently with a decrease of nitrite, giving a ratio of 1:1-1:1.3 in ammonium removal rate over nitrite consumption rate. A continuous-mode mesophilic fixed-bed reactor was established to enrich the AAAO consortium. After 1 year, biofilms, pinkish in color, had developed on the support media and side wall of the feed-line tubing. Ammonium and nitrite consumption increased from ∼15 mg to 60 mg d-1 L-1 over a period of 243 days. Later, transmission electron microscopy (TEM) and fluorescence in situ hybridization (FISH) techniques revealed that the dominant cell type in the AAAO consortium had a similar morphology and 16S rDNA sequence homology to that of the recently described ANAMMOX organism, "Brocadia anammoxidans". [ABSTRACT FROM AUTHOR]

Investigates the persistence of two model enteric virions, bacteroides fragilis phage and coliphage, within pipe biofilms in an urban distribution system. How biofilms were allowed to develop on uPVC and stainless steel (SS) coupons in a modified Robbins' device for 70 d within a 150 mm uPVC reticulation main; Characteristics of the virion loss/inactivation from biofilm; Reactions followed by an initial rapid phase.

Discusses how a model for virus decay on lettuce and carrot crops has been derived as part of a comprehensive wastewater irrigation microbial risk assessment model under development. Results from the decay modeling about the presence of a persistent sub-population of viruses evidenced by an initial rapid phase of decay followed by a slow phase; How virus counts fitted a negative binomial rather than Poisson distribution indicating over-dispersion; Investigation of the implications of over-dispersion and the presence of a very persistent sub-population of viruses for assessing viral illness from the consumption of lettuces and carrots irrigated with secondary treated effluent.

Optimisation of nutrient removal processes requires a detailed understanding of the microbial physiologies actually occurring within the biomass of different treatment zones, and also knowledge of how thesecommunities respond to environmental factors. This paper describes asuite of four independent and complementary, microbiological techniques, utilised to obtain detailed assessments of wastewater bacterial biomass. Examples of these techniques are shown as applied to biofilms from two surface-flow wetlands used for treating sewage effluent. Intact biofilms were prepared via freezing, followed by cryosectioningand direct microscopic observation. This approach was combined with prior, in situ incubation of biofilm with radiolabelled thymidine to assess in situ bacterial growth rates. Individual bacterial cells were assessed microscopically for in situ respiratory activity and phylogenetic identity, respectively through use of an inducibly-fluorescent redox stain (CTC), and fluorescent in situ hybridisation (FISH) of ribosomal RNA (rRNA). These complementary techniques enabled assessment of individual biofilm clusters according to their in situ status (growth, respiration, spatial location and phylogenetic affiliation). This approach detected significant spatial variations in biofilm; limited the bias inherent in data obtained using any one technique, and provided greater detail of subpopulations within the microbial community. [ABSTRACT FROM AUTHOR]

Aims: Study the response of microbial communities and selected petroleum hydrocarbon (PH)-degrading genes on simulated PH spills in soils/sediments from different geographic locations., Methods and Results: A microcosm experiment was conducted by spiking mixtures of petroleum hydrocarbons (PHs) to soils/sediments collected from four different regions of China, including the Dagang Oilfield (DG), Sand of Bohai Sea (SS), Northeast China (NE) and Xiamen (XM). Changes in bacterial community and the abundance of PH-degrading genes (alkB, nah and phe) were analysed by denaturing gradient electrophoresis (DGGE) and qPCR, respectively. Degradation of alkanes and PAHs in SS and NE materials were greater (P < 0·05) than those in DG and XM. Clay content was negatively correlated with the degradation of total alkanes by 112 days and PAHs by 56 days, while total organic carbon content was negatively correlated with initial degradation of total alkanes as well as PAHs. Abundances of alkB, nah and phe genes increased 10- to 100-fold and varied by soil type over the incubation period. DGGE fingerprints identified the dominance of α-, β- and γ-Proteobacteria (Gram -ve) and Actinobacteria (Gram +ve) bacteria associated with degradation of PHs in the materials studied., Conclusion: The geographic divergence resulting from the heterogeneity of physicochemical properties of soils/sediments appeared to influence the abundance of metabolic genes and community structure of microbes capable of degrading PHs., Significance and Impact of the Study: When developing practical in-situ bioremediation approaches for PHs contamination of soils/sediment, appropriate microbial community structures and the abundance of PH-degrading genes appear to be influenced by geographic location., (© 2017 The Society for Applied Microbiology.)