Search

The vast majority of microorganisms in aquifers live as biofilms on sediment surfaces, which presents significant challenges for sampling as only the suspended microbes will be sampled through normal pumping. The use of a down-well low frequency sonicator has been suggested as a method of detaching microbes from the biofilm and allowing rapid sampling of this community. We developed a portable, easy to use, low-frequency electric sonicator and evaluated its performance for a range of well depths (tested up to 42 m below ground level) and casing types. Three sonicators were characterized in laboratory experiments using a 1 m long tank filled with pea gravel. These included a commercially available pneumatic sonicator, a rotating flexible shaft sonicator, and the prototype electric sonicator. The electric sonicator detached between 56 and 74% of microbes grown on gravel-containing biobags at distances ranging between 2 and 50 cm from the sonicator. The field testing comprises of a total of 55 sampling events from 48 wells located in 4 regions throughout New Zealand. Pre- and post-sonication samples showed an average 33 times increase in bacterial counts. Microbial sequence data showed that the same classes are present in pre- and post-sonicated samples and only slight differences were seen in the proportions present. The sampling process was rapid and the significant increases in bacterial counts mean that microbial samples can be quickly obtained from wells, which permits more detailed analysis than previously possible.

The present study describes the development of a laboratory-scale waste stabilisation pond (WSP) system, undertaken in order to investigate the effects of hydraulic, physicochemical, microbial and physical parameters on wastewater treatment. Previous studies have focused predominantly on hydraulic characteristics. This system was engineered at a scale much smaller than had previously been seen in the literature. The scale of the model used here allows for improved optimisation at a shorter time scale that would be seen for larger pilot-scale systems. Additionally, with the addition of viruses, a smaller scale model allows for more control over viral concentration used. Once constructed, the system was dosed with wastewater from a wastewater treatment plant and both the influent and effluent were monitored using common testing methods as well as direct viral analysis. Successful wastewater treatment was seen in terms of reduction of indicator bacteria and virus, as determined by culture-based methods. This treatment and the associated stabilisation of physicochemical parameters such as dissolved oxygen and pH, indicates the successful development of a microbial community within the laboratory-scale WSP.

This study compared light and dark disinfection of faecal bacteria/viral indicator organisms (E. coli and MS2 (fRNA) bacteriophage) and human viruses (Echovirus and Norovirus) in Wastewater Treatment Pond (WTP) mesocosms. Stirred pond mesocosms were operated in either outdoor sunlight-exposed or laboratory dark conditions in two experiments during the austral summer. To investigate wavelength-dependence of sunlight disinfection, three optical filters were used: (1) polyethylene film (light control: transmitting all solar UV and visible wavelengths), (2) acrylic (removing most UVB 5-log E. coli and MS2 phage removal (from ~1.0 × 106 to

AIM Infiltration experiments aimed to show the effectivity of coral sand to remove micro-organisms in septic tank wastewater treatment system, in South Tarawa, Kiribati. METHODS AND RESULTS Laboratory experiments evaluated effective microbial removal properties of a packed bed of coral beach sand conditioned with domestic effluent. Bacterial and viral indicators Escherichia coli J6-2, Enterococci faecalis and f-RNA (MS2) bacteriophage, along with viral pathogens adenovirus, echovirus, norovirus and rotavirus, were dosed (at 106 -107 CFU, PFU or genome copies per ml concentration) with effluent to unsaturated coral sand-packed columns. For the conditions simulated, all organisms showed removal efficiencies of >4-Log Removal Values (LRVs) (i.e. >99·99% effective reduction in number). Results revealed that the conditioned coral sand had a higher affinity for attenuating viruses than the bacteria tested. MS2 phage, adenovirus, echovirus, norovirus and rotavirus were absent in leachate from the base of the sand columns. E. coli J6-2 and E. faecalis were recovered at 100 -101 CFU (colony forming units) per ml in the column effluent, following a dosage of 106 CFU per ml. Destructive sampling of the columns after experiments revealed that a high proportion of viral pathogens were retained in the top 30 mm of the sand. CONCLUSIONS On the basis of the relative spatial distribution of trace organisms in the sand, we speculate that adsorption processes likely dominated attenuation of the viral pathogens, more so than physical straining effects. Further study is required to fully elucidate the removal mechanisms. SIGNIFICANCE AND IMPACT OF THE STUDY To the best of our knowledge this is the first study of the effective microbial removal capacity of coral sand under unsaturated conditions. The work represents an initial exploratory step of developing some standardized design practice of on-site wastewater treatment systems in Kiribati, to offer enhanced protection of groundwater resources and reduce diarrhoeal disease.

Groundwater is used as a precious resource for drinking water worldwide. Increasing anthropogenic activity is putting increasing pressure on groundwater resources. One impact of increased groundwater abstraction coupled with increasing dry weather events is the lowering of groundwater levels within aquifers. Biofilms within groundwater aquifers offer protection to the groundwater by removing contaminants entering the aquifer systems from land use activities. The study presented investigated the impact of desiccation events on the biofilms present in groundwater aquifers using field and laboratory experiments. In both field and laboratory experiments a reduction in enzyme activity (glucosidase, esterase and phosphatase) was seen during desiccation compared to wet controls. However, comparing all the data together no significant differences were seen between either wet or desiccated samples or between the start and end of the experiments. In both field and laboratory experiments enzyme activity recovered to start levels after return to wet conditions. The study shows that biofilms within groundwater systems are resilient and can withstand periods of desiccation (4 months).

Biochemical oxygen demand (BOD) is an international regulatory environmental index for monitoring organic pollutants in wastewater and the current legislated standard test for BOD monitoring requires 5 days to complete (BOD5 test). We are developing a rapid microbial technique, MICREDOX®, for measuring BOD by eliminating oxygen and, instead, quantifying an equivalent biochemical co-substrate demand, the co-substrate being a redox mediator. Elevated concentrations of Proteus vulgaris, either as free cells or immobilised in Lentikat® disks, were incubated with an excess of redox mediator (potassium hexacyanoferrate(III)) and organic substrate for 1 h at 37 °C without oxygen. The addition of substrate increased the catabolic activity of the microorganisms and the accumulation of reduced mediator, which was subsequently re-oxidised at a working electrode generating a current quantifiable by a coulometric transducer. The recorded currents were converted to their BOD5 equivalent with the only assumption being a fixed conversion of substrate and known stoichiometry. Measurements are reported both for the BOD5 calibration standard solution (150 mg l−1 glucose, 150 mg l−1 glutamic acid) and for filtered effluent sampled from a wastewater treatment plant. The inclusion of a highly soluble mediator in place of oxygen facilitated a high ferricyanide concentration in the incubation, which in turn permitted increased concentrations of microorganisms to be used. This substantially reduced the incubation time, from 5 days to 1 h, for the biological oxidation of substrates equivalent to those observed using the standard BOD5 test. Stoichiometric conversion efficiencies for the oxidation of the standard substrate by P. vulgaris were typically 60% for free cells and 35–50% for immobilised cells.

The combination of electrochemical, optical, acoustical and other measurement techniques with the specificity of biological recognition systems has resulted in a range of new analytical devices known as biosensors. Biosensors are under intensive development worldwide because they have a multitude of potential applications, in particular, clinical medicine, environmental monitoring and process control of industrial processes. Their basic principles, mode of operation, performance requirements and current trends will be reviewed. A brief description of a novel biosensor developed at Lincoln Technology, the MICREDOX method, is outlined and applications for rapid measurement of biochemical oxygen demand and toxicity measurements are described. Preliminary data obtained using the MICREDOX method are reported for three standard toxic materials, zinc sulphate, 3, 5-dichlorophenol and sodium lauryl sulphate.

This paper describes the in situ response of groundwater biofilms in an alluvial gravel aquifer system on the Canterbury Plains, New Zealand. Biofilms were developed on aquifer gravel, encased in fine mesh bags and suspended in protective columns in monitoring wells for at least 20 weeks. Four sites were selected in the same groundwater system where previous analyses indicated a gradient of increasing nitrate down the hydraulic gradient from Sites 1 to 4. Measurements during the current study classified the groundwater as oligotrophic. Biofilm responses to the nutrient gradients were assessed using bioassays, with biomass determined using protein and cellular and nucleic acid staining and biofilm activity using enzyme assays for lipid, carbohydrate, phosphate metabolism, and cell viability. In general, biofilm activity decreased as nitrate levels increased from Sites 1 to 4, with the opposite relationship for carbon and phosphorus concentrations. These results showed that the groundwater system supported biofilm growth and that the upper catchment supported efficient and productive biofilms (high ratio of activity per unit biomass).

MICREDOX is a rapid microbial-based assay, which was originally developed at Lincoln Technology to monitor biochemical oxygen demand (BOD).[1] The assay is characterized by high levels of biocatalyst (microorganisms) and redox mediator; these facilitate a fast reaction in which the microbial oxidation of an organic substrate is coupled with the reduction of the mediator. Previous efforts toward optimizing this assay have principally been directed at the selection and performance of different bacterial strains, either singly[2] or as a consortium.[3] Here we report the effect of adding a second mediator to the assay by comparing the coulombic responses and the substrate stoichiometric conversion efficiencies. Escherichia coli and half-strength standard BOD substrate (75 mg glucose L−1, 75 mg glutamic acid L−1; GGA) were incubated for one hour at 37°C in the absence of oxygen with an excess of redox mediator, potassium hexacyanoferrate(iii) (HCF), either individually or as a binary mixture that included a secondary mediator. Secondary redox mediators investigated were p-benzoquinone (BQ), 2,6-dichlorophenolindophenol (DPIP), menadione (MD), neutral red (NR), N,N′-tetramethyl-1,4-phenylenediamine (N-TMPD), phenazine ethosulphate (PES), and 2,3,5,6-tetramethyl-1,4-phenylenediamine (TMPD). When HCF was supplemented with TMPD or PES the stoichiometric conversion efficiency for the oxidation of the GGA by E. coli increased, whereas when supplemented with N-TMPD, MD, DCIP, or BQ the conversion efficiency decreased. No effect was evident when NR was used as the supplement.