Mikael Pell

Metabolic Profiles and Genetic Diversity of Denitrifying Communities in Activated Sludge after Addition of Methanol or Ethanol

ABSTRACT External carbon sources can enhance denitrification rates and thus improve nitrogen removal in wastewater treatment plants. The effects of adding methanol and ethanol on the genetic and metabolic diversity of denitrifying communities in activated sludge were compared using a pilot-scale plant with two parallel lines. A full-scale plant receiving the same municipal wastewater, but without external carbon source addition, was the reference. Metabolic profiles obtained from potential denitrification rates with 10 electron donors showed that the denitrifying communities altered their preferences for certain compounds after supplementation with methanol or ethanol and that methanol had the greater impact. Clone libraries of nirK and nirS genes, encoding the two different nitrite reductases in denitrifiers, revealed that methanol also increased the diversity of denitrifiers of the nirS type, which indicates that denitrifiers favored by methanol were on the rise in the community. This suggests that there might be a niche differentiation between nirS and nirK genotypes during activated sludge processes. The composition of nirS genotypes also varied greatly among all samples, whereas the nirK communities were more stable. The latter was confirmed by denaturing gradient gel electrophoresis of nirK communities on all sampling occasions. Our results support earlier hypotheses that the compositions of denitrifier communities change during predenitrification processes when external carbon sources are added, although no severe effect could be observed from an operational point of view.

The fertilizing effect of compost and biogas residues from source separated household waste

The fertilizing effect of compost and anaerobic residues from source separated household waste

Potential denitrification activity assay in soil—With or without chloramphenicol?

Abstract A common way to characterize denitrification in soil is to determine the potential denitrifying activity (PDA). Our objectives were to compare different techniques of mathematically describing experimental data obtained in the PDA assay, both with and without use of chloramphenicol (CAP), and to quantify the effect of CAP on the process. The PDA assay was carried out in the presence of acetylene in slurries of three agricultural soils containing 1 m m glucose and 1 m m KNO 3 . When CAP was not used in the assay, growth related curves of N 2 O-formation were obtained for all three soils. These data were used to calculate the initial rate by: (1) assuming the initial phase to be linear and using the four first data points for linear regression; and by (2) using a growth-assciated product formation equation. The good fit to the data that was obtained with the latter method suggests that PDA is a continuous process without distinct phases. Moreover, our results clearly show that denitrifying activity is inhibited by CAP even at the lowest concentration tested, 20 mg 1 −1 . The inhibiting effect increased with increasing concentrations of CAP. The PDA was 17–42% lower at 1 g CAP 1 −1 compared with assays without CAP. This shows that not only synthesis of new enzymes is affected but also that the activity of already existing enzymes is decreased. Results from our study strongly suggest that single concentrations of CAP must not be used in PDA assays. An alternative strategy could be to use multiple CAP concentrations and then extrapolate to the rate at 0 g CAP 1 −1 . However, we recommend assays without CAP and that data should be fitted to the growth-associated product formation equation. By using this method, values of the PDA and the growth rate of the denitrifying bacterial population are objectively obtained.

METABOLIC PROPERTIES OF DENITRIFYING BACTERIA ADAPTING TO METHANOL AND ETHANOL IN ACTIVATED SLUDGE

Abstract The effect of external carbon sources on metabolic properties of the denitrifying community in single-sludge systems with predenitrification was investigated. Sludge samples were collected from full-scale and pilot-scale experimental lines during microbial adaption to methanol and ethanol, respectively. Changes in functional properties were studied by measuring denitrification capacity with different electron donors in batch tests using the acetylene inhibition technique. Substrate-use profiles were analysed with principal component analysis. Adaptation to methanol was slow, and the capacity to denitrify with acetate decreased continuously. Short-chain fatty acids were less popular for denitrifiers in the methanol-adapted sludge than they were in the reference sludge, while the capacity to denitrify with methanol and ethanol was higher. Denitrification capacity with ethanol and acetate in the ethanol adapting sludge increased rapidly. The ethanol-adapted sludge also had a higher capacity to denitrify with butyrate, glycerol, and methanol. Neither methanol nor ethanol as external carbon affected denitrification capacity with aromatic compounds or glucose. A reduced ability to denitrify with a vast number of electron donors can be regarded as a negative characteristic, since it reflects a lower capacity to make use of substances in the sewage.

Activity and composition of ammonia oxidizing bacterial communities and emission dynamics of NH3 and N2O in a compost reactor treating organic household waste

Aims:  To monitor emissions of NH3 and N2O during composting and link these to ammonia oxidation rates and the community structure of ammonia oxidizing bacteria (AOB).

Adaptation of denitrifying bacteria to acetate and methanol in activated sludge

Adaptation of denitrifying bacteria to the external carbon sources acetate and methanol was studied in bench-scale sequencing batch reactors. The reactors were seeded with sludge from a full-scale pre-denitrifying activated sludge plant and operated in cycles consisting of a 23.5 h anoxic period followed by 23 h aeration. A control reactor received no additional carbon. Potential denitrification rate, measured with the acetylene inhibition technique, and the most probable number of bacteria denitrifying with the specific carbon source were followed for 52 days. Actual rates in the reactors were estimated from cumulative gas production during anoxic operation. A period of adaptation was necessary when methanol or acetate was the supplemental carbon source. Adaptation to acetate was also observed in the control reactor. The acetate sludge was, however, probably better adapted to acetate as evidenced by the greater increase in activity per bacterium. The increase continued even after the maximum denitrification rate was reached. During adaptation to methanol the methanol denitrifying capacity per bacterium was fairly constant while the potential rate increased after an initial lag-phase. Sewage water without external carbon did not cause an increased methanol activity that could be interpreted as adaptation. We suggest that the bacteria denitrifying with acetate could be the same as those using the electron donors in the sewage. The bacteria in the methanol reactor seemed to consist of one population denitrifying with methanol and another with compounds in the sewage.

Microbial numbers and activity during infiltration of septic-tank effluent in a subsurface sand filter

Abstract A subsurface, 4-person sand-filter system for treating septic-tank effluent was subjected to conventional water analysis and to an extended microbial analysis of the filter material. Measured rates of CO 2 production in the filter material suggest that the system has a good microbial capacity to degrade the organic matter in wastewater; the volume effectively treated depends on the BOD (e.g. 951 m −2 day −1 at a BOD of 169 mg l −1 and 285 l m −2 at a BOD of 74 mg l −1 ). The actual load was 40 to 80 l m −2 day −1 . Based on viable counts of bacteria the amounts of P and N bound in the 13 ± 10 g dw m −2 viable biomass were calculated to correspond to the amounts produced by 1 person in m −2 , indicating that the viable biomass also gives an accurate estimate of the active biomass. The levels of ATP in the sand-filter surface revealed that the loading of wastewater occurred unevenly. The high numbers of ammonium-oxidizing bacteria (4 × 10 3 −6 x 10 6 g −1 dw) and denitrifying bacteria (2 × 10 7 −1 =× 10 9 g −1 dw) in the surface layer show that the system was predominantly operating aerobically and had a high potential for removing nitrogen. The microbial techniques used were sensitive enough to detect the decrease in biomass that occurred with increasing depth. Reduction of COD, P and N in the wastewater during infiltration were estimated to be 86, 70 and 60% respectively. These figures are considered to be overestimates, since analysis of Cl showed that groundwater had leaked into the bed, diluting the effluent water. A correction factor for the dilution effect was therefore introduced. In addition, N and P from the surrounding arable land periodically leaked into the bed. The environment in the sand filter was sufficiently stable to ensure high microbial activity; thus the purifying capacity of septic-tank effluent should remain high throughout the year.

Microbial adaptation, process performance and a suggested control strategy in a pre-denitrifying system with ethanol dosage

Biological nitrogen removal in activated sludge processes is dependent on sufficient supplies of easily metabolized carbon compounds for the denitrifying bacterial population. An external carbon source can increase denitrification rates and compensate for deficiencies in the influent C/N ratio. Plant performance and microbial adaptation were studied in a pre-denitrifying pilot-scale activated sludge plant with and without ethanol. Total nitrogen removal efficiency was 67 and 35% for the ethanol and reference line, respectively. The process responded rapidly to ethanol but one sludge age was necessary for full bacterial adaptation. An initial rapid increase suggests enzyme induction rather than alterations in bacterial species composition. Increased enzyme activity was explained by an increase in turn-over rate of biomass. Low effluent nitrate concentration was a result of the simultaneous use of influent COD and ethanol. Fluctuations in influent COD did not affect denitrification capacity with ethanol. Sludge settling properties were moderately better in the process without ethanol addition. An automatic control strategy for carbon dosage using feedforward from influent carbon and nitrate in the recirculated flow was simulated. Simulations with an adaptive linear quadratic controller demonstrated that the desired nitrate concentration at the end of the anoxic zone could be maintained despite relatively large disturbances.

Greenhouse gas emissions from home composting in practice

In Sweden, 16% of all biologically treated food waste is home composted. Emissions of the greenhouse gases CH4 and N2O and emissions of NH3 from home composts were measured and factors affecting these emissions were examined. Gas and substrate in the compost bins were sampled and the composting conditions assessed 13 times during a 1-year period in 18 home composts managed by the home owners. The influence of process parameters and management factors was evaluated by regression analysis. The mean CH4 and N2O concentration was 28.1 and 5.46 ppm (v/v), respectively, above the ambient level and the CH4:CO2 and N2O:CO2 ratio was 0.38% and 0.15%, respectively (median values 0.04% and 0.07%, respectively). The home composts emitted less CH4 than large-scale composts, but similar amounts of N2O. Overall NH3 concentrations were low. Increasing the temperature, moisture content, mixing frequency and amount of added waste all increased CH4 emissions.

Comparative characterization of digestate versus pig slurry and cow manure – Chemical composition and effects on soil microbial activity

The growing number of biogas plants in Europe has resulted in increased production of nutrient-rich digestate with great potential as fertilizer for arable land. The nutrient composition of digestate varies with the substrate treated in the biogas plant and may contain compounds that stimulate or inhibit soil microbial activity. This study compared 20 digestates (D) with 10 pig slurries (PS) and 10 cow manures (CM) regarding their chemical content and their effect on soil microbial activities, i.e. potential ammonia oxidation rate (PAO) and soil respiration. The results showed no significant differences within the D group when divided based on substrate type. i.e. manure dominated vs. other organic waste materials in any of the tests. In general D contained significantly higher concentrations of ammonium while the concentrations of total carbon and volatile fatty acids were higher in PS and CM than in D. The D showed both stimulating and inhibiting effects on PAO, while all CM and all PS except one showed inhibiting effects on PAO. However, PAO activity was negatively correlated with the content of volatile fatty acids in the residues indicating that these compounds may be the cause of the inhibition. The maximum respiration activity (hpeakmax) was lower and the time point for the maximum respiration activity (tpeakmax) occurred earlier for D compared with CM and PS. This earlier peak time could be indicative of a high proportion of easily degradable carbon in D compared with PS and CM. However, the utilization rate of carbon, i.e. the proportion of added organic C converted to CO2-C during 12days, did not differ significantly between D, PS and CM, indicating that overall carbon quality in the different fertilizers was still roughly comparable. In short, our results suggest that digestates were different compared with PS and CM but without posing a higher risk with respect to their impact on soil microbial activity.