Pavel Svehla

Composition and parameters of household bio-waste in four seasons.

Bio-waste makes up almost half portion of municipal solid waste. The characterization of household bio-waste is important in determining the most appropriate treatment method. The differences in composition and parameters of bio-waste derived from urban settlement (U-bio-waste) and family houses (F-bio-waste) during the four climate seasons are described in this paper. Twelve components and 20 parameters for bio-waste were evaluated. The composition of U-bio-waste was almost steady over those seasons, unlike F-bio-waste. U-bio-waste was comprised mainly (58.2%) of fruit and vegetable debris. F-bio-waste was primarily made up of seasonal garden components. The amount of variation among seasons in both type of bio-waste increased in sequence: basic parameters<macro-elements<potentially toxic elements. Spearmans correlations among proportions of individual components and parameters of bio-waste were found out. Results of this research could be utilized to support another composition and parameters of bio-waste and be suitable for establishing bio-waste processing.

Effect of composting on the mobility of arsenic, chromium and nickel contained in kitchen and garden waste

The study was focused on evaluation of possible changes in As, Cr, and Ni mobility and fractionation during composting of kitchen and garden waste. Fresh bio-waste taken up seasonally was thoroughly mixed with woodchips in the wet weight portion of 3:1 and the mixture was put into batch-wise aerated fermenters under 3 air flow rates. An increased drop in exchangeable Cr and Ni was found in kitchen and garden waste after 12 weeks of composting, respectively. The exchangeable content of As decreased only during kitchen waste composting. The order of fractions in the final compost was as follows: residual>oxidizable>exchangeable>reducible. The proportion of Cr and Ni in exchangeable fraction decreased after composting more than 3- and 4-fold, respectively. Results proved that an intensive composting process is a suitable method for immobilization of Cr and Ni, and for decreasing total As contained in household bio-waste.

Inhibition effect of free ammonia and free nitrous acid on nitrite-oxidising bacteria during sludge liquor treatment: influence of feeding strategy

The importance of feeding strategy for the long-term selective inhibition of nitrite-oxidising bacteria (NOB) was demonstrated by comparison of laboratory-scale bioreactors: Completely Stirred Tank Reactor (CSTR) and Sequencing Batch Reactor (SBR). Moreover, the effect of the change of reactor operation regime from CSTR to SBR was demonstrated. Sludge liquor containing ammonia nitrogen in a range of 970–1500 mg L−1 was the influent of the reactors. The experiments were performed at (23 ± 2)°C, with high concentration of dissolved oxygen (up to 8 mg L−1) and with unlimited sludge retention time. In the SBR, permanent restriction of NOB activity was achieved for more than 700 days by the strong inhibition effect of fluctuating concentrations of free ammonia and free nitrous acid during the operational cycles of SBR. In contrast, nitrite-oxidising bacteria were able to gradually adapt to the conditions prevailing in CSTR and produce nitrate although the concentration of free ammonia and free nitrous acid significantly exceeded inhibition limits for NOB activity in this system. Transferring the reactor operation regime from CSTR to SBR resulted in immediate and permanent inhibition of NOB activity in the reactor.

The impact of influent total ammonium nitrogen concentration on nitrite-oxidizing bacteria inhibition in moving bed biofilm reactor

The application of nitrification-denitrification over nitrite (nitritation-denitritation) with municipal (i.e. diluted and cold (or low-temperature)) wastewater can substantially improve the energy balance of municipal wastewater treatment plants. For the accumulation of nitrite, it is crucial to inhibit nitrite-oxidizing bacteria (NOB) with simultaneous proliferation of ammonium-oxidizing bacteria (AOB). The present study describes the effect of the influent total ammonium nitrogen (TAN) concentration on AOB and NOB activity in two moving bed biofilm reactors operated as sequencing batch reactors (SBR) at 15 °C (SBR I) and 21 °C (SBR II). The reactors were fed with diluted reject water containing 600, 300, 150 and 75 mg TAN L(-1). The only factor limiting NOB activity in these reactors was the high concentrations of free ammonia and/or free nitrous acid (FNA) during the SBR cycles. Nitrite accumulation was observed with influents containing 600, 300 and 150 mg TAN L(-1) in SBR I and 600 and 300 in SBR II. Once nitrate production established in the reactors, the increase of influent TAN concentration up to the original 600 mg TAN L(-1) did not limit NOB activity. This was due to the massive development of NOB clusters throughout the biofilm that were able to cope with faster formation of FNA. The results of the fluorescence in situ hybridization analysis preliminarily showed the stratification of bacteria in the biofilm.

Nitrification in a completely stirred tank reactor treating the liquid phase of digestate: The way towards rational use of nitrogen

The nitrification of the liquid phase of digestate (LPD) was conducted using a 5L completely stirred tank reactor (CSTR) in two independent periods (P1 - without pH control; P2 - with pH control). The possibility of minimizing nitrogen losses during the application of LPD to the soil as well as during long-term storage or thermal thickening of LPD using nitrification was discussed. Moreover, the feasibility of applying the nitrification of LPD to the production of electron acceptors for biological desulfurization of biogas was assessed. Despite an extremely high average concentration of ammonia and COD in LPD reaching 2470 and 9080mg/L, respectively, nitrification was confirmed immediately after the start-up of the CSTR. N-NO3- concentration reached 250mg/L only two days after the start of P1. On the other hand, P1 demonstrated that working without pH control is a risk because of the free nitrous acid (FNA) inhibition towards nitrite oxidizing bacteria (NOB) resulting in massive nitrite accumulation. Up to 30.9mg/L of FNA was present in the reactor during P1, where the NOB started to be inhibited even at 0.15mg/L of FNA. During P2, the control of pH at 7.0 resulted in nitrogen oxidation efficiency reaching 98.3±1.5% and the presence of N-NO3- among oxidized nitrogen 99.6±0.4%. The representation of volatile free ammonia within total nitrogen was reduced more than 1000 times comparing with raw LPD under these conditions. Thus, optimum characteristics of the tested system from the point of view of minimizing the nitrogen losses as well as production of electron acceptors for the desulfurization of biogas were gained in this phase of reactor operation. Based on the results of the experiments, potential improvements and modifications of the tested system were suggested.

Effect of influent nitrogen concentration on feasibility of short-cut nitrification during wastewater treatment in activated sludge systems

The inhibitory effect of free ammonia and free nitrous acid on nitrite-oxidising bacteria (NOB) was studied in a laboratory-scale sequencing batch reactor with a suspended microbial culture. The reactor was operated at 15°C, with a dissolved oxygen concentration in excess of 5 mg L−1 and a nitrogen-loading rate of 0.2 kg m−3 d−1. Diluted reject water with varying total ammonia nitrogen (TAN) concentrations was used as influent. N-NO2− represented more than 90 % of all of the oxidised nitrogen, with influent TAN concentrations of 600 mg L−1, 300 mg L−1 and 150 mg L−1, respectively. With a TAN concentration of 75 mg L−1, a gradual increase in N-NO3− concentration was detected, indicating the threshold value enabling short-cut nitrification (SN) to be between 150 mg L−1 and 75 mg L−1 under the pertaining conditions. Next, the influent concentration of TAN was gradually increased from 75 mg L−1 to 1000 mg L−1 but the nitrite accumulation was not restored. This indicates that once NOB are established in the suspended microbial culture, even high TAN concentrations are not sufficient for NOB inhibition.

The Role of Aeration Intensity, Temperature Regimes And Composting Mixture on Gaseous Emission During Composting

The aim of the work was to compare production of N2O during composting with different temperature regimes, different aeration intensity and different input mixture. Two different mixtures of organic material with three levels of aeration underwent the composting process in two temperature regimes. Mixture A contained woodchips, separated pig slurry, fresh grass and tree leaves. Mixture B contained woodchips, tree leaves, grass and urea to optimize C:N ratio. This experiment was carried out in specially designed 70 liter fermentors. Oxygen and nitrous oxide were monitored in the exhaust air as well as pH, NO3− and NH4+ and temperature of solid material. The mixture with urea additive showed high N2O production when kept under low temperature; when the same mixture was kept in higher temperature, production of NO2 was 3 fold lower. However, the mixture without urea addition kept in high temperature shows almost no N2O production. Production of N2O was highest when nitrates concentration increased. Production of N2O is perhaps a by-product of nitrification, but also other pathways may contribute.

Anaerobic digestion of grass: the effect of temperature applied during the storage of substrate on the methane production

ABSTRACT Within this research, biogas production, representation of methane in biogas and volatile solids (VSs) removal efficiency were compared using batch tests performed with the samples of intensively and extensively planted grasses originating from public areas. Before the batch tests, the samples were stored at different temperatures achievable on biogas plants applying trigeneration strategy (−18°C, +3°C, +18°C and +35°C). Specific methane production from intensively planted grasses was relatively high (0.33–0.41 m3/kg VS) compared to extensively planted grasses (0.20–0.33 m3/kg VS). VSs removal efficiency reached 59.8–68.8% for intensively planted grasses and 34.6–56.5% for extensively planted grasses. Freezing the intensively planted grasses at −18°C proved to be an effective thermal pretreatment leading to high biogas production (0.61 m3/kg total solid (TS)), high representation of methane (64.0%) in biogas and good VSs removal efficiency (68.8%). The results of this research suggest that public areas or sport parks seem to be available, cheap and at the same time very effective feedstock for biogas production.

How biomass growth mode affects ammonium oxidation start-up and NOB inhibition in the partial nitritation of cold and diluted reject water

ABSTRACT The inhibition of undesirable nitrite oxidizing bacteria (NOB) and desirable ammonium oxidizing bacteria (AOB) by free ammonia (FA) and free nitrous acid (FNA) in partial nitritation (PN) is crucially affected by the biomass growth mode (suspended sludge, biofilm, encapsulation). But, the limitations of these modes towards less concentrated reject waters (≤600 mg-N L−1) are unclear. Therefore, this work compares the start-up and stability of three PN sequencing batch reactors (SBRs) with biomass grown in one of the three modes: suspended sludge, biofilm and biomass encapsulated in polyvinyl alcohol (PVA) pellets. The SBRs were operated at 15°C with influent total ammonium nitrogen (TAN) concentrations of 75–600 mg-TAN L−1. PN start-up was twice as fast in the biofilm and encapsulated biomass SBRs than in the suspended sludge SBR. After start-up, PN in the biofilm and suspended sludge SBRs was stable at 150–600 mg-TAN L−1. But, at 75 mg-TAN L−1, full nitrification gradually developed. In the encapsulated biomass SBR, full nitrification occurred even at 600 mg-TAN L−1, showing that NOB in this set-up can adapt even to 4.3 mg-FA L−1 and 0.27 mg-FNA L−1. Thus, PN in the biofilm was best for the treatment of an influent containing 150–600 mg-TAN L−1.

Properties of vermicompost aqueous extracts prepared under different conditions

ABSTRACT The aim of this work was to determine the influence of aeration and time of extraction on the agrochemical properties of aqueous extracts from vermicomposts made from horse manure (M) and apple pomace (P) waste. There were two extract treatments: stirring without aeration (S), and stirring with aeration (A) for 48 h. Aeration significantly increased the levels of electrical conductivity (EC) and the concentration of , , and macro-elements in the extracts. In the (A) treatment, the extraction efficiency of K and Mg increased twofold, and the extraction efficiency of Ca and P increased by one-third compared with the (S) treatment. Simultaneously, the extracts prepared under aeration were characteristic with a higher pH value compared with non-aerated variants. The EC and content of macro-elements in the extracts increased proportionally with time. Their highest growth was found within the first 6 h. After 48 h, the highest release of macro-elements into the extract was found in the case of the horse manure under stirring with aeration.