Natural wetlands contribution on phosphorus removal in small northern communities in Canada.

This study focuses on understanding the role of passive wastewater treatment (wastewater lagoon plus wetland) in reducing the phosphorus discharge levels in a northern small community in Manitoba, Canada. The facultative lagoon system of that small community treats domestic wastewater and seasonally discharges effluent into a wetland that connects to Lake Manitoba. This research assesses phosphorus removal efficiency through the natural wetland during the vegetation growing season. The average total phosphorus (TP) concentration reduction for the observed treatment area of 1.3 ha was more than 70%, achieving the desired TP discharge concentration below 1 mg/L. Data analysis showed that the main accumulation of TP occurred at the 21-40 cm soil depth, which indicates the potential of natural wetland treatment applications under cold continental climate conditions as an effluent polishing step to satisfy regulatory requirements for phosphorus reduction.

Aluminum phosphate sludge as a phosphorus source for maize production under low soil phosphorus availability.

Background: With increasing food demand as a consequence of the growing world population, there is a corresponding demand for additional sources of phosphorus (P). Alum-phosphate (Al-P) sludge is a by-product of wastewater treatment and can be a good source of P. In this study, the response of maize (Zea mays L.) to Al-P sludge was tested. Maize was chosen as the test crop due to its prevalent use as human and animal food and as a source of biofuel. The objective of the study was to investigate Al-P sludge as a source of P compared to a commercial fertilizer (monoammonium phosphate, MAP). Methods: A growth chamber assay was conducted over four cropping cycles (45 d each). The application rate was 9.7, 19.4, 29.1 and 38.8 mg P kg-1 dry soil. Amendments were applied once at the start of the first cropping cycle. Plants were harvested after each cycle and pots were re-seeded. Dry matter yield (DMY), total P uptake, Al-P uptake, soil total P and Olsen-P concentrations, pH, and EC were measured. Results: DMY was significantly greater in pots amended with Al-P sludge than in pots treated with MAP. There was a significant rate × cropping cycle interaction effect on DMY with the differences among rates in cycle 1 different from those in cycle 4. Phosphorus uptake depended on cropping cycle, P source and P application rate. With sludge uptake higher than MAP in all cycles, the highest P uptake was observed at the highest application rate except for cycle 2 where this was observed at the rate of 29.1 mg kg-1. For MAP, phosphorus recovery efficiency (PRE) at the highest rate was significantly greater than that at the lowest rate whereas PRE in cycle 1 was significantly higher than that in cycle 4. In the first two cycles, aluminum uptake was negligible in both MAP and Al-P sludge treatments; however, in cycles 3 and 4, there was significantly more Al in maize from sludge amended pots. Our results show that Al-P sludge was as effective as MAP in supplying enough P for biomass yield. We, therefore, conclude that Al-P sludge could be an alternative source of P, especially for growing maize as feedstock for bioenergy.

Bioavailability study of phosphorus in alum-phosphorus sludge using switchgrass.

The study investigated biomass yield and the uptake of P and aluminum by switchgrass grown in a low-P soil amended with alum-P sludge and a conventional fertilizer, monoammonium phosphate (MAP), at rates of 9.7, 19.4, 29.1 and 38.8 mg P kg-1 dry soil. Potted soil (amended and control) units were seeded with pre-germinated switchgrass and harvested three times at 50-day intervals. Over the three growth cycles, P from alum-P sludge gradually became available. Amendment rate showed no significant effect on switchgrass biomass yield. P availability was greater for alum-P sludge than MAP and this may have been enhanced by the properties and activities of the plant root system. Aluminum (Al) uptake by switchgrass increased with the number of cycles, but did not differ significantly among treatments. Cumulative Al uptake over the 3 cycles was greater for below-ground biomass than for above-ground biomass. Maximum P recovery efficiency of 28% was achieved at the 9.7 mg P kg soil-1 rate. These results demonstrate that alum-P sludge is an effective source of available P for cropping switchgrass in a high pH and low Olsen-P soil.

Statistical modeling of phosphorus solubilization from chemical sludge and evaluation of optimal sodium hydroxide dose.

Phosphorus (P) recovery from sludge has drawn widespread attention across the world to minimize the P load to the watershed, a concern for eutrophication, and to meet the stringent effluent discharge regulations in some countries. Waste activated sludge (WAS) and dewatered sludge (DS) were treated with a wide range of NaOH doses (0-0.75 g g-1 TS). The WAS sludge was diluted to 4.5%-2.25% of TS before the treatment to make comparable amount of TS as of DS (2.25%-1.5%). The kinetic study illustrated that P solubilization reached equilibrium within the first 20 min of treatment duration. Significant positive correlation was found between solution pH and P solubilization, whereas effect of TS was mostly insignificant. The experimental data was well fitted to the exponential models and exhibited maximum P solubilization of about 67% and 56% from the DS and WAS at NaOH doses of 0.71 and 0.27 g g-1 TS, respectively. The optimal NaOH application dose of 0.36 g g-1 TS for DS and 0.20 g g-1 TS for WAS were obtained with 64% and 48% of P solubilization, respectively. The modeling approach and the optimal dose of NaOH illustrated in this study could be utilized for other types of sludges having similar P to TS ratio and P solubilization mechanisms could be further extended to other type of P recovery techniques.

Seasonal variations in cold climate nutrient removal: A comparison of facultative and aerated lagoons.

The seasonal trends in standard wastewater parameters are studied for two lagoons in the Canadian Prairies; one facultative and one aerated with the purpose of better understanding the underlying biological mechanisms in place. In particular, treatment in a cold climate is examined as treatment efficiency and function vary with geographical latitude. It was found that during the winter season, nutrients are not removed and nutrient release is observed. At the arrival of spring, biological growth occurs leading to spring awakening of the lagoons whereby nutrients start to again be removed. Phosphorus is removed by biomass assimilation and precipitation. It was found that these mechanisms were not very effective at treating this nutrient and additional treatment is required. Nitrogen is removed mainly by air stripping and its concentration is influenced by both temperature and pH, the latter of which is greatly affected by algae growth.

Overall effect of carbon production and nutrient release in sludge holding tank on mainstream biological nutrient removal efficiency.

The potential of hydrolysis/fermentation of activated sludge in sludge holding tank (SHT) to produce additional carbon for the biological nutrient removal (BNR) process was investigated. The study was conducted in anaerobic batch tests using the BNR sludge (from a full-scale Westside process) and the mixture of BNR sludge with conventional non-BNR activated sludge (to have higher biodegradable particulate chemical oxygen demand (bpCOD) in sludge). The BioWin 4.1 was used to simulate the anaerobic batch test of the BNR sludge. Also, the overall effect of FCOD production and nutrient release on BNR efficiency of the Westside process was estimated. The experimental results showed that the phosphorous uptake of sludge increased during hydrolysis/ fermentation condition up to the point when poly-P was completely utilized; afterwards, it decreased significantly. The BioWin simulation could not predict the loss of aerobic phosphorous uptake after poly-P was depleted. The results showed that in the case of activated sludge with relatively higher bpCOD (originating from plants with short sludge retention time or without primary sedimentation), beneficial effect of SHT on BNR performance is feasible. In order to increase the potential of SHT to enhance BNR efficiency, a relatively low retention time and high sludge load is recommended.

Simplified empirical model for phosphorous removal in a facultative wastewater lagoon.

Nutrient removal in a facultative lagoon in Manitoba, Canada, was monitored from May 2015 to April 2016. According to the 12-month data, phosphorous concentration in the effluent did not meet the regulatory requirement. Various models have been developed to predict nitrogen removal from lagoon through the years; however, not much effort has been deployed to model phosphorous removal from lagoons. Therefore, this research aims to relate the lagoon phosphate removal to the volatile suspended solids (VSS), metal concentration, and detention time. A simple empirical equation was derived by observing the one-year data, which considers assimilation into biomass as a major mechanism of phosphorous removal. The metals' concentration was found to be very low in the facultative lagoon studied. Hence, phosphorous precipitation by metals was neglected. The model relates assimilation directly to VSS which is simple to evaluate practically unlike other models that require individual algae and bacteria concentration. The correlation coefficient (R2) between the observed and the predicted effluent VSS was 0.92, which indicates excellent fit. The R2 between observed and predicted effluent orthophosphate was 0.83, which indicates moderate fit. The trend of modeled effluent phosphate is similar to the observed effluent phosphate concentration, which approves the validity of this model. The model developed in this research can be used to predict the average effluent VSS and phosphorous concentration in similar facultative lagoons.

Study on the effect of landfill leachate on nutrient removal from municipal wastewater.

In this study, landfill leachate with and without pre-treatment was co-treated with municipal wastewater at different mixing ratios. The leachate pre-treatment was achieved by air stripping to removal ammonia. The objective of this study was to investigate the effect of landfill leachate on nutrient removal of the wastewater treatment process. It was demonstrated that when landfill leachate was co-treated with municipal wastewater, the high ammonia concentration in the leachate did not have a negative impact on the nitrification. The system was able to adapt to the environment and was able to improve nitrification capacity. The readily biodegradable portion of chemical oxygen demand (COD) in the leachate was utilized by the system to improve phosphorus and nitrate removal. However, this portion was small and majority of the COD ended up in the effluent thereby decreased the quality of the effluent. The study showed that the 2.5% mixing ratio of leachate with wastewater improved the overall biological nutrient removal process of the system without compromising the COD removal efficiency.

Influence of carbon source on nutrient removal performance and physical-chemical characteristics of aerobic granular sludge.

The impact of carbon source variation on the physical and chemical characteristics of aerobic granular sludge and its biological nutrient (nitrogen and phosphorus) removal performance was investigated. Two identical sequencing batch reactors, R1 and R2, were set up. Granular biomass was cultivated to maturity using acetate-based synthetic wastewater. After mature granules in both reactors with simultaneous chemical oxygen demand (COD), ammonium and phosphorus removal capability were achieved, the feed of R2 was changed to municipal wastewater and R1 was continued on synthetic feed as control. Biological phosphorus removal was completely inhibited in R2 due to lack of readily biodegradable COD; however, the biomass maintained high ammonium and COD removal efficiencies. The disintegration of the granules in R2 occurred during the first two weeks after the change of feed, but it did not have significant impacts on settling properties of the sludge. Re-granulation of the biomass in R2 was then observed within 30 d after granules' disintegration when the biomass acclimated to the new substrate. The granular biomass in R1 and R2 maintained a Sludge Volume Index close to 60 and 47 mL g(-1), respectively, during the experimental period. It was concluded that changing the carbon source from readily biodegradable acetate to the more complex ones present in municipal wastewater did not have significant impacts on aerobic granular sludge characteristics; it particularly did not affect its settling properties. However, sufficient readily biodegradable carbon would have to be provided to maintain simultaneous biological nitrate and phosphorus removal.

Effect of dissolved oxygen on biological nutrient removal by denitrifying phosphorus-accumulating organisms in a continuous-flow system.

A laboratory-scale continuous-flow system with an anaerobic/anoxic/aerobic configuration was set up to study the effect of oxygen in the internal recycle stream; of particular interest was its performance of denitrifying phosphorus-accumulating organisms (DPAOs). It was found that, by using a degas device, the dissolved oxygen in the nitrate recycle stream was effectively decreased from 0.1 +/- 0.02 to 0.01 +/- 0.01 mg/L. This provided a favorable condition for DPAOs to grow under an anoxic condition and thus be sustained successfully in the system. When the degas device was removed from the system, the dissolved oxygen concentration in the anoxic reactor increased to 0.1 +/- 0.02 mg/L. The proliferation of the denitrifying glycogen-accumulating organisms (DGAOs) population and deterioration of DPAOs performance was observed. The increased population of DGAO/GAOs, which competed for the carbon source with DPAO/ PAOs, resulted in a poor performance of biological phosphorus removal.

Low temperature biological phosphorus removal and partial nitrification in a pilot sequencing batch reactor system.

Partial nitrification and biological phosphorus removal appear to hold promise of a cost-effective and sustainable biological nutrient removal process. Pilot sequencing batch reactors (SBRs) were operated under anaerobic/aerobic configuration for 8 months. It was found that biological phosphorus removal can be achieved in an SBR system, along with the partial nitrification process. Sufficient volatile fatty acids supply was the key for enhanced biological phosphorus removal. This experiment demonstrated that partial nitrification can be achieved even at low temperature with high dissolved oxygen (>3 mg/L) concentration. Shorter solid retention time (SRT) for nitrite oxidizing bacteria (NOB) than for ammonia oxidizing bacteria due to the nitrite substrate limitation at the beginning of the aeration cycle was the reason that caused NOB wash-out. Controlling SRT should be the strategy for an SBR operated in cold climate to achieve partial nitrification. It was also found that the aerobic phosphorus accumulating organisms' P-uptake was more sensitive to nitrite inhibition than the process of anaerobic P-release.

Interaction between denitrification and phosphorus removal in a sequencing batch reactor phosphorus removal system.

Batch experiments were performed to investigate simultaneous denitrification and phosphorus removal by denitrifying phosphorus accumulating organisms (DNPAO). The results showed that while using the same amount of carbon source, DNPAOs are able to uptake phosphorus by using nitrate as an electron acceptor. It was observed that higher nitrate concentration required a longer anoxic period for denitrifying phosphate uptake. In addition, the effect of the presence of nitrate in substrate was studied. Phosphorus release occurred as long as substrate was present in the anaerobic phase regardless of nitrate concentrations. It also was noticed that nitrate hindered the release of phosphorus in the anaerobic stage because of denitrifiers competing with phosphorus accumulating organisms for their carbon source. The DNPAOs, however, remained competitive in a system with nitrate in the anaerobic phase.