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.
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.
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.
The comparative importance of macro-invertebrates and attachment of faecal coliform (FC) to suspended matter (particulate and plant material) in the removal of FC in three types of domestic ...wastewater treatment pond system was investigated. The three pond types, connected in series of four ponds were fully duckweed ponds, fully algal ponds and a hybrid of two duckweed ponds sandwiching two algal ponds, all on a pilot scale. Attachment of FC to suspended matter was more important at the bottom of the first two ponds with duckweed having 256 and 99% for pond 1 and 2, algal ponds having 946 and 75% and hybrid pond system having significant attachment at the bottom only in pond 2 (71%). Significantly greater FC decay rates in algal ponds (p<0.05) were observed in the afternoons (12.6, 10.0 and 3.6) compared with the mornings (7.1, 1.7 and 2.7) for ponds 1, 2 and 4 respectively. High numbers of ostracods in ponds 1–4 (29,867±143.6, 6151±426.3, 934±258.8 and 594±16.3) were associated with the surface of all the duckweed ponds and these were significantly higher than that of algal ponds (0, 2±2, 0, 0) at similar locations (p<0.05). FC numbers in the duckweed pond systems correlated strongly and positively with total ostracod numbers in pond (R2=0.989) and at the surface (R2=0.996) but not at the bottom. This suggests that macro-invertebrate feeding and movement activity could be a good contributor to the removal of FC in duckweed ponds. FC numbers also correlated negatively (duckweed R2=−0.71; algal R2=−0.80 and hybrid R2=−0.66) with the Shannon–Wiener diversity index of macro-invertebrates, an indicator of pond water quality.
Co-disposal of septic tank sludge had a positive effect on the municipal solid waste (MSW) stabilisation process in Bioreactor Landfill simulators. Co-disposal experiments were carried out using the ...Bioreactor Landfill approach aiming to solve the environmental problems caused by indiscriminate and inadequate disposal of MSW and especially of septic tank sludge. The simulator receiving septic tank sludge exhibited a 200 days shorter lag-phase as compared to the 350 days required by the control simulator to start the exponential biogas production. Additionally, the simulator with septic sludge apparently retained more moisture (>60% w/w), which enhanced the overall conversion of organic matter hence increasing the biogas production (0.60
m
3
biogas
kg
−1
VS
converted) and removal efficiency of 60% for VS from the simulator. Alkaline pH values (pH
>
8.5) did not inhibit the biogas production; moreover it contributed to reduce partially the negative effects of NH
4
+ (>2
g
L
−1) due to NH
3 volatilisation thus reducing the nitrogen content of the residues. Associated risks and hazards with septage disposal were practically eliminated as total coliform and faecal coliform contents were reduced by 99% and 100%, respectively at the end of the experiment. These results indicate that co-disposal has two direct benefits, including the safe and environmentally sound disposal of septic tank sludge and an improvement of the overall performance of the Bioreactor Landfill by increasing moisture retention and supplying a more acclimatised bacterial population.
The effect of algal density on faecal coliform (FC) decay under conditions of light and darkness were monitored in low and medium strength wastewater and in a ‘mixture of treated and raw wastewater’ ...depicting conditions of a variety of dissolved organic compounds. Rates of decay of FC varied in darkness with varying chlorophyll-a concentrations, supporting the hypothesis that algae may produce substances that are toxic to FC. The first empirical evidence that an optimum chlorophyll-a concentration (10 ± 2 mg L
−1
) for maximum FC destruction in wastewater exist is reported. Rate of decay was higher in medium strength wastewater compared with low strength wastewater at higher algal densities of ≥13.9 mg L
−1
chlorophyll-a both in light and in darkness, while addition of fresh wastewater to an ongoing wastewater treatment process may lower the rate of FC decay for a wide range of algal densities (0.6–19.6 mg L
−1
), under light conditions.
A simple and reliable method to measure the activity of ammonia and nitrite oxidisers in mixed bacterial cultures was developed. The developed method differentiates between the ammonia and nitrite ...oxidisers by consecutive injection of NO2- and NH4+. The main advantage of this method is that it avoids the use of metabolic inhibitors for ammonia or nitrite oxidisers, as used by other methods. Moreover, it allows measuring of the short-term effect of an inhibitor on both the ammonia and nitrite oxidisers in one test under controlled environmental conditions (pH, temperature). The developed method was applied to determine the inhibitory effects of salt (NaCl up to 15 g Cl/l) on an enriched culture of nitrifying bacteria. The results of the method demonstrate its potential to accurately determine the individual activities of nitrite and ammonia oxidisers.
Seven bioreactor landfill simulators (mixed gravel, gravel in layers, and controls without gravel with two levels of compaction, i.e. normal and lower density) were used to investigate the effect of ...different hydraulic conditions on the waste stabilisation process. The simulators with mixed gravel showed a higher degree of waste stabilisation towards the end of the experiment due to higher moisture content, whereas the other simulators were prone to clogging thus reducing the overall treatment effectiveness. Moreover, reaching neutral pH levels seemed to be the "driving force" that enhanced physical, chemical and biological processes contributing to waste stabilisation in the simulators with mixed gravel. After one year of operation, the residues of the different simulators were very close to achieve a final storage quality status comparable to the waste acceptance criteria for inert waste of the European landfill directive.
A bench-scale continuous-flow wastewater treatment system comprising three parallel lines using duckweed (Spirodela polyrhiza), water lettuce (Pistia stratiotes), and algae (natural colonization) as ...treatment agents was set up to determine environmental conditions, fecal coliform profiles and general treatment performance. Each line consisted of four ponds connected in series fed by diluted sewage. Influent and effluent parameters measured included environmental conditions, turbidity, biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrate, nitrite, ammonia, total phosphorus, fecal coliforms, mosquito larvae, and sludge accumulations. Environmental conditions and fecal coliforms profiles were determined in the sediments (0.63 m), suspensions (0.35 m), and surfaces (0.1 m) of each pond. Acidic conditions were observed in the pistia ponds, neutral conditions in duckweed ponds, and alkaline conditions in algal ponds. Fecal coliforms log removals of 6, 4, and 3 were observed in algal, duckweed, and pistia ponds, respectively, in the final effluents, with die-off rates per pond of 2.7, 2.0, and 1.6. Sedimentation accounted for over 99% fecal coliform removal in most of the algal and pistia ponds. BOD removal was highest in the duckweed system, followed by pistia and algae at 95%, 93%, and 25%, respectively. COD removals were 65% and 59%, respectively, for duckweed and pistia, while COD increased in algal ponds by 56%. Nitrate removals were 72%, 70%, and 36%, respectively for duckweed, pistia, and algal ponds. Total phosphorus removals were 33% and 9% for pistia and duckweed systems, while an increase of 19% was observed in the algal treatment system. Ammonia removals were 95% in both pistia and duckweed and 93% in algal systems. Removals of total dissolved solids (TDS) were 70% for pistia, 15% for duckweed, and 9% for algae. Mosquito populations of 11,175/m
2
, 3516/m
2
, and 96/m
2
were counted in pistia, algal, and duckweed ponds, respectively. Low turbidity and low sludge accumulation characterized the macrophyte ponds. Performance in the removal of fecal coliforms in the algal-based treatment system and organic load removal in both macrophytes and algal-based treatment systems met the Ghana Environmental Protection Agency guideline values.
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