The influence of different carbon sources (acetate to propionate ratios), temperature and pH levels on the competition between polyphosphate- and glycogen-accumulating organisms (PAO and GAO, ...respectively) was evaluated using a metabolic model that incorporated the carbon source, temperature and pH dependences of these microorganisms. The model satisfactorily described the bacterial activity of PAO (
Accumulibacter) and GAO (
Competibacter and
Alphaproteobacteria-GAO) laboratory-enriched cultures cultivated on propionate (HPr) and acetate (HAc) at standard conditions (20
°C and pH 7.0). Using the calibrated model, the effects of different influent HAc to HPr ratios (100–0, 75–25, 50–50 and 0–100%), temperatures (10, 20 and 30
°C) and pH levels (6.0, 7.0 and 7.5) on the competition among
Accumulibacter,
Competibacter and
Alphaproteobacteria-GAO were evaluated. The main aim was to assess which conditions were favorable for the existence of PAO and, therefore, beneficial for the biological phosphorus removal process in sewage treatment plants. At low temperature (10
°C), PAO were the dominant microorganisms regardless of the used influent carbon source or pH. At moderate temperature (20
°C), PAO dominated the competition when HAc and HPr were simultaneously supplied (75–25 and 50–50% HAc to HPr ratios). However, the use of either HAc or HPr as sole carbon source at 20
°C was not favorable for PAO unless a high pH was used (7.5). Meanwhile, at higher temperature (30
°C), GAO tended to be the dominant microorganisms. Nevertheless, the combined presence of acetate and propionate in the influent (75–25 and 50–50% HAc to HPr ratios) as well as a high pH (7.5) appear to be potential factors to favor the metabolism of PAO over GAO at higher sewage temperature (30
°C).
The effect of salinity on the activity, the composition of nitrifiers and floc characteristics of nitrifying sludge was studied. Non-adapted and adapted (to 10
g NaCl–Cl
−/L for one year) enriched ...cultures of nitrifiers were tested in three sequencing batch reactors. Salt was increased gradually with 5 up to 40
g Cl
−/L.
No difference in steady state activity was observed between the adapted and non-adapted sludge. The activities of ammonia and nitrite oxidizers dropped 36% and 11%, respectively, at salt concentrations of 10
g Cl
−/L. At 40
g
Cl
−/L inhibition reached 95% of salt free activity for ammonia and nitrite oxidizers in both adapted and non-adapted reactors.
Nitrosomonas europaea and
Nitrobacter sp. (fluorescent in situ hybridization) were the only nitrifiers present at high salt levels. Increased salt concentrations resulted in better settling characteristics of the nitrifying sludge. After 118 days the sludge was brought back to the initial conditions (0
g
Cl
−/L for non-adapted and 10
g Cl
−/L for adapted). Despite the change in population composition similar kinetics as before the salt stress were observed.
The influence of operating and environmental conditions on the microbial populations of the enhanced biological phosphorus removal (EBPR) process at seven full-scale municipal activated sludge ...wastewater treatment plants (WWTPs) in The Netherlands was studied. Data from the selected WWTPs concerning process configuration, operating and environmental conditions were compiled. The EBPR activity from each plant was determined by execution of anaerobic–anoxic–aerobic batch tests using fresh activated sludge. Fractions of Accumulibacter as potential phosphorus accumulating organisms (PAO), and Competibacter, Defluviicoccus-related microorganisms and Sphingomonas as potential glycogen accumulating organisms (GAO) were quantified using fluorescence in situ hybridization (FISH). The relationships among plant process configurations, operating parameters, environmental conditions, EBPR activity and microbial populations fractions were evaluated using a statistical approach. A well-defined and operated denitrification stage and a higher mixed liquor pH value in the anaerobic stage were positively correlated with the occurrence of Accumulibacter. A well-defined denitrification stage also stimulated the development of denitrifying PAO (DPAO). A positive correlation was observed between Competibacter fractions and organic matter concentrations in the influent. Nevertheless, Competibacter did not cause a major effect on the EBPR performance. The observed Competibacter fractions were not in the range that would have led to EBPR deterioration. Likely, the low average sewerage temperature (12±2°C) limited their proliferation. Defluviicoccus-related microorganisms were seen only in negligible fractions in a few plants (<0.1% as EUB), whereas Sphingomonas were not observed.
As an initial part of a programme aimed at promoting safe and sound agricultural practices in Ghana, a study was made of farmers' perceptions of pesticides for use and application in vegetable ...production, using a small survey of 137 farmers who applied pesticides. Field surveys, interviews, questionnaires and analytical games were used to obtain information on the type, scope and extent of use of pesticides, farmers' knowledge of pesticides, and their perceptions about the chemicals' potential for harm. Data from this sample of farmers were used to describe the status of use of pesticides in vegetable cultivation in Ghana. Using chi2 tests, associations between farmers' age and possible pesticide poisoning symptoms, their farm size and method of spraying pesticides, and their perception of pesticide hazard and its perceived effectiveness against pests were also examined. The survey showed that knapsack sprayers were the most widely used type of equipment for spraying pesticides. However, on large-scale vegetable farms of 6-10 acres, motorised sprayers were also used. Various inappropriate practices in the handling and use of pesticides caused possible poisoning symptoms among those farmers who generally did not wear protective clothing. Younger farmers (<45 years of age) were the most vulnerable group, probably because they did more spraying than older farmers (>45 years of age). Farmers did not necessarily associate hazardous pesticides with better pest control. The introduction of well-targeted training programmes for farmers on the need for and safe use of pesticides is advocated.
Glycogen accumulating organisms (GAO) compete for substrate with polyphosphate-accumulating organisms (PAO), which are the microorganisms responsible for the enhanced biological phosphorus removal ...(EBPR) in activated sludge wastewater treatment systems. This can lead to the deterioration of the EBPR process. In this paper, the long-term temperature effects on the anaerobic and aerobic stoichiometry and conversion rates on adapted enriched cultures of
Competibacter (a known GAO) were evaluated from 10 to 40
°C. The anaerobic stoichiometry of
Competibacter was constant from 15 to 35
°C, whereas the aerobic stoichiometry was insensitive to temperature changes from 10 to 30
°C. At 10
°C, likely due to the inhibition of the anaerobic conversions of
Competibacter, a switch in the dominant bacterial population to an enriched
Accumulibacter culture (a known PAO) was observed. At higher temperatures (35 and 40
°C), the aerobic processes limited the growth of
Competibacter. Due to the inhibition or different steady-state (equilibrium) conditions reached at long-term by the metabolic conversions, the short- and long-term temperature dependencies of the anaerobic acetate uptake rate of
Competibacter differed considerably between each other. Temperature coefficients for the various metabolic processes are derived, which can be used in activated sludge modeling. Like for PAO cultures: (i) the GAO metabolism appears oriented at restoring storage pools rather than fast microbial growth, and (ii) the aerobic growth rate of GAO seems to be a result of the difference between PHA consumption and PHA utilization for glycogen synthesis and maintenance. It appears that the proliferation of
Competibacter in EBPR systems could be suppressed by adjusting the aerobic solids retention time while, aiming at obtaining highly enriched PAO cultures, EBPR lab-scale reactors could be operated at low temperature (e.g. 10
°C).
A mathematical model describing the interaction between nitrifiers, heterotrophs and predators in wastewater treatment has been developed. The inclusion of a predation mechanism is a new addition to ...the existing activated sludge models. The developed model considered multi-substrate consumption and multi-species growth, maintenance and decay in a culture where nitrifiers, heterotrophs and predators (protozoa and metazoa) are coexisting. Two laboratory-scale sequenced batch reactors (SBRs) operated at different sludge retention time (SRT) of 30 and 100 days for a period of 4 years were used to calibrate and validate the model. Moreover, to assess the predator activity, a simple procedure was developed, based on measuring the respiration rate with and without the presence of the predators. The model successfully described the performance of two SBRs systems. The fraction of active biomass (ammonia oxidisers, nitrite oxidisers and heterotrophs) predicted by the proposed model was only 33% and 14% at SRT of 30 and 100 days, respectively. The high fraction of inert biomass predicted by the model was in accordance with the microscopic investigations of biomass viability in both reactors. The presented model was used to investigate the effect of increasing sludge age and the role of predators on the biomass composition of the tested SBR system.
Eutrophication and its accompanying algal development in lakes is a nuisance and may be problematic for aquatic life, but limited algal development may have some beneficial consequences. Dissolved ...oxygen concentration and pH increases attributed to algae in algal-based treatment ponds may occur in eutrophic lakes and can result in the inactivation of faecal coliforms in eutrophic lakes. We investigated the die-off of Escherichia coli placed in dialysis tubes in a eutrophic lake at different depths and locations. The importance of E. coli attachment to algae and suspended matter was also assessed. Algal presence in the lake resulted in significant decay of E. coli. At chlorophyll a concentration ≤0.08mgL−1 in Weija Lake, decay rate of E. coli is directly proportional to the chlorophyll a concentration of the lake. Under laboratory conditions, as chlorophyll a concentration increases in light however, an optimum chlorophyll a concentration (0.24mg/L) is reached after which the rate of decay of E. coli decreases. These results show that limited algal presence representing optimum chlorophyll a concentration in restored ecosystems may have public health benefits for rural communities in developing countries that depend on raw water for domestic activities.
Nitrogen removal processes and nitrogen mass balances in algae-based ponds (ABPs) and duckweed (
Lemna gibba)-based ponds (DBPs) were assessed during periods of 4 months, each under different ...operational conditions. During periods 1 and 2, the effect of cold and warm temperature was studied. During periods 2 and 3, the effect of low- and high-system organic loading (OL) was studied in warm seasons operation. The pilot-scale systems consisted of four similar ponds in series fed with domestic sewage with hydraulic retention time of 7 days in each pond. Overall nitrogen removal was higher during warm temperature in both ABPs and DBPs, but similar during periods 2 and 3. Nitrogen removal in DBPs was lower than in ABPs by 20%, 12% and 8% during cold temperature, warm temperature and high-OL periods, respectively. Depending on temperature and OL rate, ABPs showed higher nitrogen removal via sedimentation (46–245% higher) compared to DBPs. Also, ABPs also showed higher nitrogen removal via denitrification (7–37% higher) compared to DBPs. Ammonia volatilisation in both systems did not exceed 1.1% of influent total nitrogen during the entire experimental period. N uptake by duckweed corresponds to 30% of the influent nitrogen during warm/low OL period and decreased to 10% and 19% during the cold and warm/high OL period, respectively. Predictive models for nitrogen removal presented a good reflection of nitrogen fluxes on overall nitrogen balance under the prevailing experimental conditions.
Entombed waste in current sanitary landfills will generate biogas and leachate when physical barriers fail in the future, allowing the intrusion of moisture into the waste mass contradicting the ...precepts of the sustainability concept. Bioreactor landfills are suggested as a sustainable option to achieve Final Storage Quality (FSQ) status of waste residues; however, it is not clear what characteristics the residues should have in order to stop operation and after-care monitoring schemes. An experiment was conducted to determine the feasibility to achieve FSQ status (Waste Acceptance Criteria of the European Landfill Directive) of residues in a pilot scale bioreactor landfill. The results of the leaching test were very encouraging due to their proximity to achieve the proposed stringent FSQ criterion after 2 years of operation. Furthermore, residues have the same characteristics of alternative waste stabilisation parameters (low BMP, BOD/COD ratio, VS content,
SO
4
2
-
/
Cl
-
ratio) established by other researchers. Mass balances showed that the bioreactor landfill simulator was capable of practically achieving biological stabilisation after 2 years of operation, while releasing approximately 45% of the total available (organic and inorganic) carbon and nitrogen into the liquid and gas phases.
Quantification of ammonia volatilisation from wastewater stabilisation ponds is important in order to understand its significance for overall nitrogen removal in these widely applied low-cost ...treatment systems. Ammonia volatilisation rates were measured in pilot plant facilities consisting of one line of four algae-based ponds in series and a parallel line of four ponds with a floating mat of duckweed (
Lemna gibba). Ammonia volatilisation was assessed during a period of one and a half years. The method applied is accurate, convenient and is proposed for analysis of a wide range of gasses emitted from stabilisation ponds and possibly other aquatic systems. The ammonia volatilisation rates in algae-based ponds (ABPs) were higher than in duckweed-based ponds (DBPs). This can be explained by the lower values of NH
3 in DBPs due to shading and lower pH values, since the volatilisation rate highly correlated with free ammonia concentration (NH
3) in pond water. The duckweed cover appeared not to provide a physical barrier for volatilisation of unionised ammonia, because whenever NH
3 concentrations were equal in ABP and DBP also the volatilisation rates were equal. Volatilisation was in the range of 7.2–37.4
mg-N
m
−2
d
−1 and 6.4 –31.5
mg-N
m
−2
d
−1 in the ABPs and DBPs, respectively. Average influent and effluent ammonium nitrogen measurements showed that the ammonia volatilisation during the study period in any system did not exceed 1.5% of total ammonium nitrogen removal. Therefore this study confirmed results from simultaneous experimental work in our laboratory indicating that nitrification/denitrification, rather than ammonia volatilisation, is the most important mechanism for N removal in ABPs and DBPs.
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