Claudia Gallert

Mesophilic and thermophilic anaerobic digestion of source-sorted organic wastes : effect of ammonia on glucose degradation and methane production

Abstract The wet organic fraction of household wastes was digested anaerobically at 37 °C and 55 °C. At both temperatures the volatile solids loading was increased from 1 g l−1 day−1 to 9.65 g l−1 day−1, by reducing the nominal hydraulic retention time from 93 days to 19 days. The volatile solids removal in the reactors at both temperatures for the same loading rates was in a similar range and was still 65% at 19 days hydraulic retention time. Although more biogas was produced in the thermophilic reactor, the energy conservation in methane was slightly lower, because of a lower methane content, compared to the biogas of the mesophilic reactor. The slightly lower amount of energy conserved in the methane of the thermophilic digester was presumably balanced by the hydrogen that escaped into the gas phase and thus was no longer available for methanogenesis. In the thermophilic process, 1.4 g/l ammonia was released, whereas in the mesophilic process only 1 g/l ammonia was generated, presumably from protein degradation. Inhibition studies of methane production and glucose fermentation revealed a Ki (50%) of 3 g/l and 3.7 g/l ammonia (equivalent to 0.22 g/l and 0.28 g/l free NH3) at 37 °C and a Ki (50%) of 3.5 g/l and 3.4 g/l ammonia (equivalent to 0.69 g/l and 0.68 g/l free NH3) at 55 °C. This indicated that the thermophilic flora tolerated at least twice as much of free NH3 than the mesophilic flora and, furthermore, that the thermophilic flora was able to degrade more protein. The apparent ammonia concentrations in the mesophilic and in the thermophilic biowaste reactor were low enough not to inhibit glucose fermentation and methane production of either process significantly, but may have been high enough to inhibit protein degradation. The data indicated either that the mesophilic and thermophilic protein degraders revealed a different sensitivity towards free ammonia or that the mesophilic population contained less versatile protein degraders, leaving more protein undegraded.

Effect of ammonia on the anaerobic degradation of protein by a mesophilic and thermophilic biowaste population

Abstract The influence of ammonia on the anaerobic degradation of peptone by mesophilic and thermophilic populations of biowaste was investigated. For peptone concentrations from 5 g l−1 to 20 g l−1 the mesophilic population revealed a higher rate of deamination than the thermophilic population, e.g. 552 mg l−1 day−1 compared to 320 mg l−1 day−1 at 10 g l−1 peptone. The final degree of deamination of the thermophilic population was, however, higher: 102 compared to 87 mg NH3/g peptone in the mesophilic cultures. If 0.5–6.5 g l−1 ammonia was added to the mesophilic biowaste cultures, deamination of peptone, degradation of its chemical oxygen demand (COD) and formation of biogas were increasingly inhibited, but no hydrogen was formed. The thermophilic biowaste cultures were most active if around 1 g ammonia l−1 was present. Deamination, COD degradation and biogas production decreased at lower and higher ammonia concentrations and hydrogen was formed in addition to methane. Studies of the inhibition by ammonia of peptone deamination, COD degradation and methane formation revealed a Ki (50%) for NH3 of 92, 95 and 88 mg l−1 at 37 °C and 251, 274 and 297 mg l−1 at 55 °C respectively. This indicated that the thermophilic flora tolerated significantly more NH3 than the mesophilic flora. In the mesophilic reactor effluent 4.6 × 108 peptone-degrading colony-forming units (cfu)/ml were culturable, whereas in the thermophilic reactor effluent growth of only 5.6 × 107 cfu/ml was observed.

Scale-up of anaerobic digestion of the biowaste fraction from domestic wastes.

In the City of Karlsruhe/Germany anaerobic digestion of 7200 ta(-1) of separately collected biowaste has proven its feasibility at an organic loading rate (OLR) of up to 8.5 kg CODm(-3)d(-1). An extension of biowaste collection over the whole city area would increase the amount of biowaste to 12,000 ta(-1), leading to an OLR of the existing anaerobic reactor of up to 15 kg CODm(-3)d(-1). To test, whether the increased amount of biowaste could be stabilized in the existing plant, biowaste suspensions were digested in a laboratory reactor at a maximum OLR, that exceeded the future OLR of the full-scale plant. The laboratory reactor was started with effluent of the full-scale biowaste digester. Like in full-scale, biowaste suspension from the hydropulper was added in a fed-batch mode. The elimination of organic material (measured as COD, chemical oxygen demand) and the volumetric gas production were linearly increasing with the OLR from 4.3 to 19 kg CODm(-3)d(-1). Thus, safe operation of the full-scale plant at an OLR of 15 kg CODm(-3)d(-1) should be possible, leaving still some reserve capacity. To determine the metabolic reserves for fatty acid degradation during digestion at an OLR of 10 kg CODm(-3)d(-1), digester effluent was supplemented with either 40 mmoll(-1) acetate, propionate, i-butyrate or n-butyrate. Results of these batch assays indicated a rapid degradation of all fatty acids and fatty acid conversion rates, that would allow a stable anaerobic fermentation at 15 kg CODm(-3)d(-1)OLR. On the basis of the laboratory results the OLR of the full-scale methane reactor was increased to 15 kg CODm(-3)d(-1). After 7 months, results of full-scale digestion were still consistent with the previously obtained laboratory results.

Effect of varying salinity, temperature, ammonia and nitrous acid concentrations on nitrification of saline wastewater in fixed-bed reactors

Nitrification under changing salinities (0-9%), temperatures (6-50°C), ammonia (0-5 g NL(-1)) and nitrite concentrations (0-0.4 g NL(-1)) was investigated in fixed-bed reactors. For all conditions ammonia oxidation rates (AOR) were lower than nitrite oxidation rates (NOR). AORs and NORs increased from 12.5 to 40°C and were very low at 6°C and almost zero at 50°C. No recovery of nitrification was obtained after incubation at 50°C, whereas nitrification was restorable after incubation at 6°C. Ammonia concentrations of 5 g NL(-1) or nitrite concentrations up to 0.125 g NL(-1) decreased AOR to almost zero. AORs and NORs recovered if ammonia or nitrite was removed. At concentrations of 1 and 5 g NL(-1) ammonia AOR and NOR were inhibited by 50%, whereas 27 mg N/L nitrite inhibited AOR by 50%.

Hazardous concentrations of selenium in soil and groundwater in North-West India

Soil and groundwater samples were collected for bulk elemental analyses in particular for selenium (Se) concentrations from six agricultural sites located in states of Punjab and Haryana in North-West India. Toxic concentrations of Se (45-341 μg L(-1)) were present in groundwater (76 m deep) of Jainpur and Barwa villages in Punjab. Selenium enrichments were also found in top soil layers (0-15 cm) of Jainpur (2.3-11.6 mg kg(-1)) and Barwa (3.1 mg kg(-1)). Mineralogical analyses confirmed silicates and phyllosilicates as main components of these soils, also reflected by the high content of SiO(2) (40-62 wt.%), Al(2)O(3) (9-21 wt.%) and K(2)O (2.2-3.2 wt.%). Prevailing intensive irrigation practices in Punjab with Se enriched groundwater may be the cause of Se accumulation in soils. Sequential extraction revealed >50% Se bioavailability in Jainpur soils. Appearance of selenite was observed in some of the batch assays with soil slurries under reducing conditions. Although safe Se concentrations were found in Hisar, Haryana, yet high levels of As, Mo and U present in groundwater indicated its unsuitability for drinking purposes. Detailed biogeochemical studies of Se in sediments or groundwater of Punjab are not available so far; intensive investigations should be started for better understanding of the problem of Se toxicity.

Antibiotic resistance of bacteria in raw and biologically treated sewage and in groundwater below leaking sewers

More than 750 isolates of faecal coliforms (>200 strains), enterococci (>200 strains) and pseudomonads (>340 strains) from three wastewater treatment plants (WTPs) and from four groundwater wells in the vicinity of leaking sewers were tested for resistance against 14 antibiotics. Most, or at least some, strains of the three bacterial groups, isolated from raw or treated sewage of the three WTPs, were resistant against penicillin G, ampicillin, vancomycin, erythromycin, triple sulfa and trimethoprim/sulfamethoxazole (SXT). Only a few strains of pseudomonads or faecal coliforms were resistant against some of the other tested antibiotics. The antibiotic resistances of pseudomonads, faecal coliforms and enterococci from groundwater varied to a higher extent. In contrast to the faecal coliforms and enterococci, most pseudomonads from all groundwater samples, including those from non-polluted groundwater, were additionally resistant against chloramphenicol and SXT. Pseudomonads from sewage and groundwater had more multiple antibiotic resistances than the faecal coliforms or the enterococci, and many pseudomonads from groundwater were resistant to more antibiotics than those from sewage. The pseudomonads from non-polluted groundwater were the most resistant isolates of all. The few surviving faecal coliforms in groundwater seemed to gain multiple antibiotic resistances, whereas the enterococci lost antibiotic resistances. Pseudomonads, and presumably, other autochthonous soil or groundwater bacteria, such as antibiotic-producing Actinomyces sp., seem to contribute significantly to the gene pool for acquisition of resistances against antibiotics in these environments.

Elimination of COD, microorganisms and pharmaceuticals from sewage by trickling through sandy soil below leaking sewers

To simulate the filtration and/or degradation of trickling sewage from leaky sewers through the non-water-saturated underground, sewage was trickled through sand of 0.4-2mm from the Rhine valley in glass columns of 125 cm length. For the same sewage the chemical oxygen demand (COD) removal was almost independent of low or high trickling rates. The COD removal efficiency varied, however, from 67% to 79%, for sewage from rain and dry weather periods, respectively. The water content of the moist sand increased from initially 80 ml kg(-1) with increasing sewage trickling rates to 108 ml kg(-1) sand. It remained at 108 ml kg(-1) at higher trickling rates higher than 600 ml d(-1). Analyses of effluent of five consecutive 25-cm soil columns revealed that about 50% of the initial COD were filtrated off on top of the sand or degraded in the uppermost 25 cm at varying trickling rates. Another 6-12% of the COD were removed in the following 25-50 cm of sand, whereas almost no further COD removal was seen in the subsequent two or three 25-cm columns. The COD elimination during trickling of sewage through the segmented column (interrupted random flow) was slightly better than that in the non-segmented column. Total and faecal coliform bacteria decreased faster with increasing trickling depth than that of total aerobic or anaerobic bacteria. After a filter/degradation stretch of 125 cm elimination of all bacteria reached 96.2-99.9%. The sewage contained low concentrations of at least 10 different pharmaceuticals or X-ray media. During trickling of sewage through sand, elimination of these compounds by adsorption onto sand and/or biodegradation varied from a complete removal, e.g. Ibuprofen or Naproxen, to almost no removal for several X-ray contrast media. Some of the medicals were removed as effectively as during conventional sewage treatment.

Co-digestion of press water and food waste in a biowaste digester for improvement of biogas production.

Co-digestion of press water from organic municipal wastes and of homogenized food residues with defibered kitchen wastes (food waste) as the main substrate was examined to improve biogas production. Although the biowaste digester was operated already at high organic loading (OLR) of 12.3 kg CODm(-3)d(-1) during the week, addition of co-substrates not only increased biogas production rates but also improved total biogas production. By feeding the two co-substrates up to 20 kg CODm(-3)d(-1) gas production followed the increasing OLR linearly. When the OLR was further increased with food waste, not more gas than for 20 kg CODm(-3)d(-1) OLR was obtained, indicating the maximum metabolic capabilities of the microbes. During weekends (no biowaste available) food waste could substitute for biowaste to maintain biogas production. Addition of press water or food waste to biowaste co-digestion resulted in more buffer capacity, allowing very high loadings without pH control.

Removal of total and antibiotic resistant bacteria in advanced wastewater treatment by ozonation in combination with different filtering techniques.

Elimination of bacteria by ozonation in combination with charcoal or slow sand filtration for advanced sewage treatment to improve the quality of treated sewage and to reduce the potential risk for human health of receiving surface waters was investigated in pilot scale at the sewage treatment plant Eriskirch, Baden-Wuerttemberg/Germany. To determine the elimination of sewage bacteria, inflowing and leaving wastewater of different treatment processes was analysed in a culture-based approach for its content of Escherichia coli, enterococci and staphylococci and their resistance against selected antibiotics over a period of 17 month. For enterococci, single species and their antibiotic resistances were identified. In comparison to the established flocculation filtration at Eriskirch, ozonation plus charcoal or sand filtration (pilot-scale) reduced the concentrations of total and antibiotic resistant E. coli, enterococci and staphylococci. However, antibiotic resistant E. coli and staphylococci apparently survived ozone treatment better than antibiotic sensitive strains. Neither vancomycin resistant enterococci nor methicillin resistant Staphylococcus aureus (MRSA) were detected. The decreased percentage of antibiotic resistant enterococci after ozonation may be explained by a different ozone sensitivity of species: Enterococcus faecium and Enterococcus faecalis, which determined the resistance-level, seemed to be more sensitive for ozone than other Enterococcus-species. Overall, ozonation followed by charcoal or sand filtration led to 0.8-1.1 log-units less total and antibiotic resistant E. coli, enterococci and staphylococci, as compared to the respective concentrations in treated sewage by only flocculation filtration. Thus, advanced wastewater treatment by ozonation plus charcoal or sand filtration after common sewage treatment is an effective tool for further elimination of microorganisms from sewage before discharge in surface waters.

Anaerobic carboxylation of phenol to benzoate: use of deuterated phenols revealed carboxylation exclusively in the C4-position

Summary[U-D]Phenol and [4-D]phenol were used to rule out carboxylation of phenol in the C1-position by a strictly anaerobic, defined mixed culture. By mass spectrometric analysis of deuterated phenol species and of benzoate, which were formed from [U-D]phenol by D/H-exchange or by carboxylation from cell suspensions, it was shown that only one deuterium (D) from the aromatic nucleus was replaced with a least 97% efficiency. This excluded benzoate synthesis by carboxylation in the C1-position of phenol. Finally, carboxylation in the para-position of phenol was demonstrated with [4-D]phenol by gas chromatography/mass spectroscopy of the products. Since direct measurement of phenol carboxylase activity was impossible due to a very active interfering decarboxylase activity, the optimal pH range and ion strength, as well as the requirement of cations in crude cell-free extracts was characterized by means of D/H-exchange from deuterated phenol.