Mari K.H. Winkler

Segregation of Biomass in Cyclic Anaerobic/Aerobic Granular Sludge Allows the Enrichment of Anaerobic Ammonium Oxidizing Bacteria at Low Temperatures

A cyclic anaerobic/aerobic bubble column reactor was run for 420 days to study the competition for nitrite between nitrite oxidizing bacteria (NOB) and anaerobic ammonium oxidizing bacteria (Anammox) at low temperatures. An anaerobic feeding period with nitrite and ammonium in the influent followed by an aerated period was applied resulting in a biomass specific conversion rate of 0.18 ± 0.02 [gN(2) - N · gVSS(-1)· day(-1)] when the dissolved oxygen concentration was maintained at 1.0 mgO(2) · L(-1). An increase in white granules was observed in the reactor which were mainly located at the top of the settled sludge bed, whereas red granules were located at the bottom. FISH, activity tests, and qPCR techniques revealed that red biomass was dominated by Anammox bacteria and white granules by NOB. Granules from the top of the sludge bed were smaller and therefore had a higher aerobic volume fraction, a lower density, and consequently a slower settling rate. Sludge was manually removed from the top of the settled sludge bed to selectively remove NOB which resulted in an increased overall biomass specific N-conversion rate of 0.32 ± 0.02 [gN(2) - N · gVSS(-1) · day(-1)]. Biomass segregation in granular sludge reactors gives an extra opportunity to select for specific microbial groups by applying a different SRT for different microbial groups.

Selective sludge removal in a segregated aerobic granular biomass system as a strategy to control PAO–GAO competition at high temperatures

An aerobic granular sludge (AGS) reactor was run for 280 days to study the competition between Phosphate and Glycogen Accumulating Organisms (PAOs and GAOs) at high temperatures. Numerous researches have proven that in suspended sludge systems PAOs are outcompeted by GAOs at higher temperatures. In the following study a reactor was operated at 30 °C in which the P-removal efficiency declined from 79% to 32% after 69 days of operation when biomass removal for sludge retention time (SRT) control was established by effluent withdrawal. In a second attempt at 24 °C, efficiency of P-removal remained on average at 71 ± 5% for 76 days. Samples taken from different depths of the sludge bed analysed using Fluorescent in situ hybridization (FISH) microscopy techniques revealed a distinctive microbial community structure: bottom granules contained considerably more Accumulibacter (PAOs) compared to top granules that were dominated by Competibacter (GAOs). In a third phase the SRT was controlled by discharging biomass exclusively from the top of the sludge bed. The application of this method increased the P-removal efficiency up to 100% for 88 days at 30 °C. Granules selected near the bottom of the sludge bed increased in volume, density and overall ash content; resulting in significantly higher settling velocities. With the removal of exclusively bottom biomass in phase four, P-removal efficiency decreased to 36% within 3 weeks. This study shows that biomass segregation in aerobic granular sludge systems offers an extra possibility to influence microbial competition in order to obtain a desired population.

The biodrying concept: An innovative technology creating energy from sewage sludge

A full-scale biodrying installation was treating 150 kton (wet weight) of dewatered waste activated sludge per year. The waste was treated at thermophilic conditions (65-75 °C) in a 2-step forced aeration process reducing the total wet sludge weight by 73%. The final product had a high caloric value (7700-10,400 (kJ/kg)), allowing a combustion for energy generation in external facilities. The resulting product met the European microbial and heavy metal quality standards needed for an application as organic fertilizer. The facility used <0.5 MW of electricity and recovered 9.3 MW from biologically produced heat, which was internally used for the heating of office buildings. Produced ammonia, originating from the microbial conversion of organic matter, was recovered from the ventilated air in an acid gas scrubber as an ammonium sulphate solution 40% (w/w) (7.3 kton/year) and was sold as substitute for artificial fertilizers. The sustainability of this process is discussed relative to other sludge handling processes.

Unravelling the reasons for disproportion in the ratio of AOB and NOB in aerobic granular sludge

In this study, we analysed the nitrifying microbial community (ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB)) within three different aerobic granular sludge treatment systems as well as within one flocculent sludge system. Granular samples were taken from one pilot plant run on municipal wastewater as well as from two lab-scale reactors. Fluorescent in situ hybridization (FISH) and quantitative PCR (qPCR) showed that Nitrobacter was the dominant NOB in acetate-fed aerobic granules. In the conventional system, both Nitrospira and Nitrobacter were present in similar amounts. Remarkably, the NOB/AOB ratio in aerobic granular sludge was elevated but not in the conventional treatment plant suggesting that the growth of Nitrobacter within aerobic granular sludge, in particular, was partly uncoupled from the lithotrophic nitrite supply from AOB. This was supported by activity measurements which showed an approximately threefold higher nitrite oxidizing capacity than ammonium oxidizing capacity. Based on these findings, two hypotheses were considered: either Nitrobacter grew mixotrophically by acetate-dependent dissimilatory nitrate reduction (ping-pong effect) or a nitrite oxidation/nitrate reduction loop (nitrite loop) occurred in which denitrifiers reduced nitrate to nitrite supplying additional nitrite for the NOB apart from the AOB.

Improved phosphate removal by selective sludge discharge in aerobic granular sludge reactors

Two lab‐scale aerobic granular sludge sequencing batch reactors were operated at 20 and 30°C and compared for phosphorus (P) removal efficiency and microbial community composition. P‐removal efficiency was higher at 20°C (>90%) than at 30°C (60%) when the sludge retention time (SRT) was controlled at 30 days by removing excess sludge equally throughout the sludge bed. Samples analyzed by fluorescent in situ hybridization (FISH) indicated a segregation of biomass over the sludge bed: in the upper part, Candidatus Competibacter phosphatis (glycogen‐accumulating organisms—GAOs) were dominant while in the bottom, Candidatus Accumulibacter phosphatis (polyphosphate‐accumulating organisms—PAOs) dominated. In order to favour PAOs over GAOs and hence improve P‐removal at 30°C, the SRT was controlled by discharging biomass mainly from the top of the sludge bed (80% of the excess sludge), while bottom granules were removed in minor proportions (20% of the excess sludge). With the selective sludge removal proposed, 100% P‐removal efficiency was obtained in the reactor operated at 30°C. In the meantime, the biomass in the 30°C reactor changed in color from brownish‐black to white. Big white granules appeared in this system and were completely dominated by PAOs (more than 90% of the microbial population), showing relatively high ash content compared to other granules. In the reactor operated at 20°C, P‐removal efficiency remained stable above 90% regardless of the sludge removal procedure for SRT control. The results obtained in this study stress the importance of sludge discharge mainly from the top as well as in minor proportions from the bottom of the sludge bed to control the SRT in order to prevent significant growth of GAOs and remove enough accumulated P from the system, particularly at high temperatures (e.g., 30°C). Biotechnol. Bioeng. 2012; 109:1919–1928.

Evaluating the solid retention time of bacteria in flocculent and granular sludge.

The specific solid retention time for different bacteria within flocculent and granular sludge was determined. Samples were collected from reactor and effluent sludge and the number of a specific bacterial group was evaluated in respect to the total bacterial community with quantitative polymerase chain reaction (qPCR). The ratio of the relative presence of a specific bacterial group in the reactor sludge and wasted sludge was established to observe if preferential wash-out occurred. From the data also the solid retention time for different microbial groups can be estimated. Using this tool, we were able to show that the SRT of populations found on the exterior of granules is slightly lower than the SRT for population in the interior. Archaea were not found in the flocculent system but were present in small amounts within the granular system. It was further observed that protozoa were grazing on the bacterial community within the system indicating that they have the potential to shorten the specific SRT of bacteria.

A full-scale house fly (Diptera: Muscidae) larvae bioconversion system for value-added swine manure reduction

Manure produced from confined animal farms can threaten public and environmental health if not managed properly. Herein, a full-scale commercial bioconversion operation in DeQing County, China for value-added swine manure reduction using house fly, Musca domestica L., larvae is reported. The greenhouse-assisted larvae bioreactor had a maximum daily treatment capacity of 35 m3 fresh raw manure per day. The bioconversion process produced a fresh larvae yield of 95–120 kg m3 fresh raw manure. This process provided an alternative animal foodstuff (having 56.9 and 23.8% protein and total fat as dry matter, respectively), as well as captured nutrients for agricultural re-utilization. Bioconversion reduced odour emission (characterized by 3-methylindole) and the Escherichia coli (E. coli) index by 94.5 and 92.0%, respectively, and reductions in total weight, moisture and total Kjeldahl nitrogen in solids were over 67.2, 80.0 and 76.0%, respectively. Yearly profit under this trial period ranged from US

Effect of the dilution rate on microbial competition : r-strategist can win over k-strategist at low substrate concentration

33.4–46.1 per m3. It is concluded that swine manure larvae bioconversion technology with subsequent production of value-added bio-products can be a promising avenue when considering a programme to reduce waste products in an intensive animal production system.

Integration of methane removal in aerobic anammox-based granular sludge reactors

The conditions present in both in vitro and in vivo ecosystems determine the microbial population harbouring it. One commonly accepted theory is that a species with a high substrate affinity and low growth rate (k-strategist) will win the competition against a second species with a lower substrate affinity and higher growth rate (r-strategist) if both species are subjected to low substrate concentrations. In this study two nitrite oxidizing bacteria (NOB), Nitrospira defluvii (k-strategist) and Nitrobacter vulgaris (r-strategist), were cultivated in a continuous reactor systems. The minimal hydraulic retention time (HRT) required for maintaining the slower growing Nitrospira was first determined. A reactor containing Nitrobacter was set to the same HRT and Nitrospira was injected to evaluate the effect of the dilution rate on the competition between both species. By following the microbial population dynamics with qPCR analysis, it was shown that not only the substrate affinity drives the competition between k- and r-strategists but also the dilution rate. Experimental data and numerical simulations both revealed that the washout of Nitrobacter was significantly delayed at dilution rates close to the μmax of Nitrospira. The competition could be even reverted towards Nitrobacter (r-strategist) despite of low nitrite concentrations and dilution rates lower than the μmax of Nitrospira.

Resource limitation modulates the fate of dissimilated nitrogen in a dual-pathway Actinobacterium

ABSTRACT Combined partial nitritation-anaerobic ammonium oxidation (anammox) processes have been widely applied for nitrogen removal from anaerobic digestion reject water. However, such streams also contain dissolved methane that can escape to the atmosphere, hence contributing to global warming. This study investigates the possibility of integrating methane removal in aerobic anammox-based granular sludge reactors, through modelling and simulation. Methane removal could be established through aerobic methane-oxidizing bacteria (MOB), denitrifying anaerobic methane-oxidizing bacteria (damoB, NO2− + CH4 → N2 + CO2), and/or archaea (damoA, NO3− + CH4 → NO2− + CO2). The simulation results demonstrated that the combined removal of nitrogen and methane was feasible at low dissolved oxygen conditions. Aerobic MOB were the main responsible microorganisms for removing methane. A sensitivity analysis of key kinetic parameters showed a shift in the methanotrophic populations depending on the most favourable parameters for each microbial group, while keeping high nitrogen and methane removal efficiencies. Possible methane stripping during aeration could be limited by increasing the depth within the reactor column at which aeration was supplied. Overall, the integration of methane removal in aerobic anammox-based granular sludge reactors seems to be a promising process option to reduce the carbon footprint from wastewater treatment. GRAPHICAL ABSTRACT