Riku Vahala

The evaluation of drinking water treatment performed with HPSEC

Characterization of natural organic matter (NOM) removal in the drinking-water treatment train can give valuable information, while optimizing the treatment process. In this study, high-performance size-exclusion chromatography (HPSEC) was applied to evaluate the relative changes of molecular size distribution (MSD) of NOM in different treatment steps. The full-scale treatment train consisting of coagulation, flocculation, sedimentation, sand filtration, and ozonation was studied in Pitkakoski water treatment plant, Helsinki, Finland. Furthermore, in a pilot-scale process, the effect of the subsequent two-step granular activated carbon (GAC) filtration on MSD was evaluated. Chemical treatment followed by sand filtration decreased NOM efficiently. The fraction of the largest molecules disappeared completely, and the next two fractions were reduced by 92% and 85%, respectively. No significant changes in the smallest molecular fractions were observed. Ozonation shifted MSD slightly towards smaller molecules, depending on the applied ozone dose. However, the increase of assimilable organic carbon (AOC) could not be related to the certain fraction of NOM. On the contrary, MSD did not change considerably during two-step GAC-filtration, except in the fresh GAC columns, where the adsorption of large molecules was slower than with smaller ones. Conversely, the smallest molecules seemed to escape from the exhausted GAC filter. Finally, significant correlations were established between HPSEC results, KMnO4 number, UV absorbance (254 nm), chlorine demand, and TOC results.

Start-up and operation of an aerobic granular sludge system under low working temperature inoculated with cold-adapted activated sludge from Finland

An aerobic granular sludge system has been started-up and operated at 7°C temperature using cold-adapted activated sludge as inoculum. The system could form granular biomass due to batch operation allowing for just 5-3min of biomass sedimentation. Scanning electron microscopy showed that fungi helped in the granular biomass formation in the early stages of the granule formation. The removal performance of the system was of 92-95% in BOD5, 75-80% in COD, 70-76% in total nitrogen and 50-60% in total phosphorous. The bacterial community structure from cold-adapted activated sludge changed during the operational time, leading to a final configuration dominated by Microbacteriaceae members Microbacterium and Leucobacter, which were strongly correlated to biomass settling velocity and bioreactor performance, as suggested by multivariate redundancy analyses. This experiment showed that aerobic granular sludge systems could be successfully started-up and operated, with high performance, under low operational temperatures when using cold-adapted biomass as inoculum.

Nitrous Oxide Production at a Fully Covered Wastewater Treatment Plant: Results of a Long-Term Online Monitoring Campaign

The nitrous oxide emissions of the Viikinmäki wastewater treatment plant were measured in a 12 month online monitoring campaign. The measurements, which were conducted with a continuous gas analyzer, covered all of the unit operations of the advanced wastewater-treatment process. The relation between the nitrous oxide emissions and certain process parameters, such as the wastewater temperature, influent biological oxygen demand, and ammonium nitrogen load, was investigated by applying online data obtained from the process-control system at 1 min intervals. Although seasonal variations in the measured nitrous oxide emissions were remarkable, the measurement data indicated no clear relationship between these emissions and seasonal changes in the wastewater temperature. The diurnal variations of the nitrous oxide emissions did, however, strongly correlate with the alternation of the influent biological oxygen demand and ammonium nitrogen load to the aerated zones of the activated sludge process. Overall, the annual nitrous oxide emissions of 168 g/PE/year and the emission factor of 1.9% of the influent nitrogen load are in the high range of values reported in the literature but in very good agreement with the results of other long-term online monitoring campaigns implemented at full-scale wastewater-treatment plants.

The effect of GAC filtration on bacterial regrowth and nitrification in a simulated water main

A 16‐month pilot study in two similar 1200 m water mains was conducted to determine the effects of granular activated carbon (GAC) filtration on drinking water quality in a distribution system. The results demonstrated that despite the higher initial disinfectant residue, the increase in bacteria in the conventionally treated and postozonated water was higher than in the water additionally treated with GAC filtration and u.v.‐disinfection. Accordingly, a significant decline in assimilable organic carbon in the postozonated water was observed throughout the main, whereas in the GAC‐filtered water this decline was shifted to the GAC filters. In the GAC‐filtered water the conversion of ammonia to nitrite and nitrite to nitrate was more intense than in postozonated water. The findings confirm that GAC filtration increases the biological stability of drinking water even when treating cold humic waters in which biodegradation is generally limited by phosphorus. However, it appears that biological treatment favours the slow kinetics of nitrifying bacteria, thus allowing nitrification to occur even under cold water conditions in a distribution system.

Nitrogen and Phosphorus Harvesting from Human Urine Using a Stripping, Absorption, and Precipitation Process

Human urine contains significant amounts of N (nitrogen) and P (phosphorus); therefore it has been successfully used as fertilizer in different crops. But the use of urine as fertilizer has several constraints, such as, the high cost of transportation, an unpleasant smell, the risk of pathogens, and pharmaceutical residue. A combined and improved N stripping and P precipitation technique is used in this study. In this technique, Ca(OH)2 is used to increase the pH of urine which converts ammonium into ammonia gas and precipitate P as Ca-P compound. The ammonia gas is stripped and passed into the sulfuric acid where ammonium sulfate and hydrogen triammonium disulfate is formed. The experiment was performed using 700 mL of urine and the pH of the urine was increased above 12. Our results showed that 85-99% of N and 99% of P (w/w) can be harvested from urine in 28 h at 40 °C and in 32 h at 30 °C. The harvested N (13% N w/w) and P (1.5% P w/w) can be used as mineral fertilizer. The economic assessment of the technique showed that the extraction of N and P from 1 m3 of pure urine can make a profit of €2.25.

Secondary clarifier conditions conducting to secondary phosphorus release in a BNR plant

A full-scale study at Pihlajaniemi BNR plant in Savonlinna Finland investigated in detail the conditions in which phosphorus release in the secondary clarifier can occur. For this purpose nutrient and ORP profiles were taken in different process conditions from the sludge blanket in the secondary clarifiers. The results show that in anaerobic conditions secondary phosphorus release can take place in the secondary clarifiers without any addition of exogenous COD. Long sludge retention time in the secondary clarifier was a prerequisite of anaerobic conditions in the sludge blanket, but retention time required varied with seasons and process conditions. Some indications of simultaneous phosphorus release and denitrification without COD input was also found. The re-absorption of the released phosphorus was observed in those parts of the sludge blanket, where nitrates were present. Even with very long sludge retention times the released phosphorus stayed inside the sludge blanket and it did not impair the effluent quality. An 18 month follow-up of the BNR process revealed, however, that occasionally dissolved phosphorus escaped from the sludge blanket. It was suggested, that this was the consequence of the missing nitrate containing layer at the upper part of the sludge blanket.

Factors Affecting the Quality of the Plant Influent and Its Suitability for Prefermentation and the Biological Nutrient Removal Process

To understand wastewater quality transformations in the sewer system, a full-scale study focused on the characteristics of the influent wastewater in a middle-sized wastewater-treatment plant receiving only municipal sewage. The objective was to identify conditions in which prefermentation prior to the biological nutrient removal (BNR) process would be useful. Prefermentation aims at increasing the fraction of readily biodegradable organic matter in the wastewater. A correlation between weather conditions and the presence of readily biodegradable organic matter in the feed wastewater was found, but contrary to the expectations, wet weather periods deteriorated the quality of the feed water more than the cold period. Moreover, influent load showed seasonal variation which changes in discharged wastewater could not explain. During the warm water period, significant biological oxidation and nitrogen removal took place in the sewer system, but the plant influent water contained readily biodegradable organic m...

Effect of sulfadiazine and trimethoprim on activated sludge performance and microbial community dynamics in laboratory-scale membrane bioreactors and sequencing batch reactors at 8°C

The effect of antibiotics sulfadiazine and trimethoprim on activated sludge operated at 8°C was investigated. Performance and microbial communities of sequencing batch reactors (SBRs) and Membrane Bioreactors (MBRs) were compared before and after the exposure of antibiotics to the synthetic wastewater. The results revealed irreversible negative effect of these antibiotics in environmentally relevant concentrations on nitrifying microbial community of SBR activated sludge. In opposite, MBR sludge demonstrated fast adaptation and more stable performance during the antibiotics exposure. Dynamics of microbial community was greatly affected by presence of antibiotics. Bacteria from classes Betaproteobacteria and Bacteroidetes demonstrated the potential to develop antibiotic resistance in both wastewater treatment systems while Actinobacteria disappeared from all of the reactors after 60 days of antibiotics exposure. Altogether, results showed that operational parameters such as sludge retention time (SRT) and reactor configuration had great effect on microbial community composition of activated sludge and its vulnerability to antibiotics. Operation at long SRT allowed archaea, including ammonium oxidizing species (AOA) such as Nitrososphaera viennensis to grow in MBRs. AOA could have an important role in stable nitrification performance of MBR‐activated sludge as a result of tolerance of archaea to antibiotics.

Full-Scale investigation of the influence of flow equalization and prefermentation on nitrification.

This article presents the findings on the effects of flow equalization and prefermentation on nitrification in a full-scale municipal plant. Existing primary clarifiers in one process train were modified for diurnal flow equalization and for a low-rate volatile fatty acid production. The performance of the biological process was compared with the parallel reference process train operated with conventional primary clarification. Only a few reports on the effects of equalization on nitrification have been published, but based on this limited knowledge, diurnal flow equalization was presumed to improve the nitrification performance. However, more constant flow conditions could not fully explain the improvements of autotrophic activity. The authors suggest that increased readily biodegradable organic matter played indirectly a role in nitrification performance. Moreover, stable flow conditions were reflected in improved sludge characteristics and offered, in addition to a levelling out of diurnal variations, a long-term buffer capacity against high hydraulic loadings.