Jaakko A. Puhakka

Anaerobic treatment in pulp- and paper-mill waste management: A review

Abstract The pulp- and paper-industry generates large volumes of highly heterogenous wastewaters containing compounds from wood or other raw material, process chemicals and compounds formed during processing. The wastewaters from mechanical pulping and secondary fiber pulping as well as the condensates from chemical and semi-chemical pulping are typically non-toxic to methanogenic degradation and contain easily degradable organic compounds. Consequently, anaerobic digestion is an attractive treatment alternative for these effluents. In addition, both primary and secondary sludges from pulp- and paper-industry wastewater treatment-plants are amenable to anaerobic digestion. In contrast, the bleaching effluents from chemical pulping, the debarking effluents as well as the CTMP effluents are likely to be inhibitory to methanogenic degradation; also their biodegrability is relatively low. dilution with other wastewater streams or detoxification by various pretreatments have been used to facilitate anaerobic treatment of these inhibitory wastewaters. the potential of the anaerobic systems for reductive dechlorination and sulfur recovery is unique and of great interest. In almost all pulp- and paper-industry full-scale applications, anaerobic treatment is followed by aerobic post-treatment. The suitability and the cost of the anaerobic-aerobic and aerobic treatment-systems are largely affected by a variety of mill-specific factors.

Phytoremediation of subarctic soil contaminated with diesel fuel

The effects of several plant species, native to northern latitudes, and different soil amendments, on diesel fuel removal from soil were studied. Plant treatments included Scots Pine (Pinus sylvestris), Poplar (Populus deltoides x Wettsteinii), a grass mixture (Red fescue, Fesuca rubra; Smooth meadowgrass, Poa pratensis and Perennial ryegrass, Lolium perenne) and a legume mixture (White clover, Trifolium repens and Pea, Pisum sativum). Soil amendments included NPK fertiliser, a compost extract and a microbial enrichment culture. Diesel fuel disappeared more rapidly in the legume treatment than in other plant treatments. The presence of poplar and pine enhanced removal of diesel fuel, but removal under grass was similar to that with no vegetation. Soil amendments did not enhance diesel fuel removal significantly. Grass roots accumulated diesel-range compounds. This study showed that utilisation of selected plants accelerates removal of diesel fuel in soil and may serve as a viable, low-cost remedial technology for diesel-contaminated soils in subarctic regions.

Biogenic hydrogen and methane production from Chlorella vulgaris and Dunaliella tertiolecta biomass

BackgroundMicroalgae are a promising feedstock for biofuel and bioenergy production due to their high photosynthetic efficiencies, high growth rates and no need for external organic carbon supply. In this study, utilization of Chlorella vulgaris (a fresh water microalga) and Dunaliella tertiolecta (a marine microalga) biomass was tested as a feedstock for anaerobic H2 and CH4 production.ResultsAnaerobic serum bottle assays were conducted at 37°C with enrichment cultures derived from municipal anaerobic digester sludge. Low levels of H2 were produced by anaerobic enrichment cultures, but H2 was subsequently consumed even in the presence of 2-bromoethanesulfonic acid, an inhibitor of methanogens. Without inoculation, algal biomass still produced H2 due to the activities of satellite bacteria associated with algal cultures. CH4 was produced from both types of biomass with anaerobic enrichments. Polymerase chain reaction-denaturing gradient gel electrophoresis profiling indicated the presence of H2-producing and H2-consuming bacteria in the anaerobic enrichment cultures and the presence of H2-producing bacteria among the satellite bacteria in both sources of algal biomass.ConclusionsH2 production by the satellite bacteria was comparable from D. tertiolecta (12.6 ml H2/g volatile solids (VS)) and from C. vulgaris (10.8 ml H2/g VS), whereas CH4 production was significantly higher from C. vulgaris (286 ml/g VS) than from D. tertiolecta (24 ml/g VS). The high salinity of the D. tertiolecta slurry, prohibitive to methanogens, was the probable reason for lower CH4 production.

Isolation and Characterization of Novosphingobium sp. Strain MT1, a Dominant Polychlorophenol-Degrading Strain in a Groundwater Bioremediation System

ABSTRACT A high-rate fluidized-bed bioreactor has been treating polychlorophenol-contaminated groundwater in southern Finland at 5 to 8°C for over 6 years. We examined the microbial diversity of the bioreactor using three 16S ribosomal DNA (rDNA)-based methods: denaturing gradient gel electrophoresis, length heterogeneity-PCR analysis, and restriction fragment length polymorphism analysis. The molecular study revealed that the process was dependent on a stable bacterial community with low species diversity. The dominant organism, Novosphingobium sp. strain MT1, was isolated and characterized. Novosphingobium sp. strain MT1 degraded the main contaminants of the groundwater, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, and pentachlorophenol, at 8°C. The strain carried a homolog of the pcpB gene, coding for the pentachlorophenol-4-monooxygenase in Sphingobium chlorophenolicum. Spontaneous deletion of the pcpB gene homolog resulted in the loss of degradation ability. Phenotypic dimorphism (planktonic and sessile phenotypes), low growth rate (0.14 to 0.15 h−1), and low-copy-number 16S rDNA genes (single copy) were characteristic of strain MT1 and other MT1-like organisms isolated from the bioreactor.

Performance and ethanol oxidation kinetics of a sulfate-reducing fluidized-bed reactor treating acidic metal-containing wastewater.

The treatment of simulated acidic wastewater (pH 2.5–5)containing sulfate (1.0–2.2 g l-1), zinc (15–340 mg l -1) and iron (57 mg l -1) was studied in a sulfate-reducing fluidized-bed reactor (FBR) at 35 °C.The original lactate feed for enrichment and maintenance of the FBRculture was replaced stepwise with ethanol over 50 days. The robustnessof the process was studied by increasing stepwise the Zn, sulfate andethanol feed concentrations and decreasing the feed pH. The following precipitation rates were obtained: 360 mg l -1 d -1 for Zn and 86 mg l -1 d -1 for Fe, with over 99.8% Zn and Fe removal, with a hydraulic retention time of 16 h. Under these conditions, 77–95% of the electrons were accepted by sulfate reduction. The alkalinity produced from ethanol oxidation increased the wastewater pH from 2.5 to 7.5–8.5. Michaelis–Menten constants (Km) determined in batch FBR experiments, were 4.3–7.1 mg l -1 and 2.7–3.5 mg l -1 for ethanol and acetateoxidation, respectively. The maximum oxidation velocities (Vmax)were 0.19–0.22 mg gVS -1 min -1 and0.033–0.035 mg gVS -1 min -1, for ethanol and acetate, respectively. In summary, the FBR process produced a good quality effluent as indicated by its low organic content and Zn and Fe concentrations below0.1 mg l -1.

Diversity of chlorophenol-degrading bacteria isolated from contaminated boreal groundwater

Abstract Chlorophenol-degrading bacteria from a long-term polluted groundwater aquifer were characterized. All isolates degraded 2,4,6-trichlorophenol and 2,3,4,6-tetrachlorophenol at concentrations detected in the contaminated groundwater (< 10 mg l–1). Pentachlorophenol was degraded by three isolates when present alone. In two gram-positive isolates, 2,3,4,6-tetrachlorophenol was required as an inducer for the degradation of pentachlorophenol. The gram-positive isolates were sensitive to pentachlorophenol, with an IC50 value of 5 mg/l. Isolates belonging to the Cytophaga/Flexibacter/Bacteroides phylum had IC50 values of 25 and 63 mg/l. Isolates belonging to α-, β- and γ-Proteobacteria generally tolerated the highest pentachlorophenol concentrations (> 100 mg/l). Polychlorophenol-degrading capacity was found in strains of Nocardioides, Pseudomonas, Ralstonia, Flavobacterium, and Caulobacter previously not known to degrade polychlorophenols. In addition, six polychlorophenol-degrading sphingomonads were found.

Anaerobic conversion of microalgal biomass to sustainable energy carriers – A review

This review discusses anaerobic production of methane, hydrogen, ethanol, butanol and electricity from microalgal biomass. The amenability of microalgal biomass to these bioenergy conversion processes is compared with other aquatic and terrestrial biomass sources. The highest energy yields (kJ g(-1) dry wt. microalgal biomass) reported in the literature have been 14.8 as ethanol, 14.4 as methane, 6.6 as butanol and 1.2 as hydrogen. The highest power density reported from microalgal biomass in microbial fuel cells has been 980 mW m(-2). Sequential production of different energy carriers increases attainable energy yields, but also increases investment and maintenance costs. Microalgal biomass is a promising feedstock for anaerobic energy conversion processes, especially for methanogenic digestion and ethanol fermentation. The reviewed studies have mainly been based on laboratory scale experiments and thus scale-up of anaerobic utilization of microalgal biomass for production of energy carriers is now timely and required for cost-effectiveness comparisons.

Ethanol and hydrogen production by two thermophilic, anaerobic bacteria isolated from Icelandic geothermal areas.

Microbial fermentations are potential producers of sustainable energy carriers. In this study, ethanol and hydrogen production was studied by two thermophilic bacteria (strain AK15 and AK17) isolated from geothermal springs in Iceland. Strain AK15 was affiliated with Clostridium uzonii (98.8%), while AK17 was affiliated with Thermoanaerobacterium aciditolerans (99.2%) based on the 16S rRNA gene sequence analysis. Both strains fermented a wide variety of sugar residues typically found in lignocellulosic materials, and some polysaccharides. In the batch cultivations, strain AK17 produced ethanol from glucose and xylose fermentations of up to 1.6 mol‐EtOH/mol‐glucose (80% of the theoretical maximum) and 1.1 mol‐EtOH/mol‐xylose (66%), respectively. The hydrogen yields by AK17 were up to 1.2 mol‐H2/ mol‐glucose (30% of the theoretical maximum) and 1.0 mol‐H2/mol‐xylose (30%). The strain AK15 produced hydrogen as the main fermentation product from glucose (up to 1.9 mol‐H2/mol‐glucose [48%]) and xylose (1.1 mol‐H2/mol‐xylose [33%]). The strain AK17 tolerated exogenously added ethanol up to 4% (v/v). The ethanol and hydrogen production performance from glucose by a co‐culture of the strains AK15 and AK17 was studied in a continuous‐flow bioreactor at 60°C. Stable and continuous ethanol and hydrogen co‐production was achieved with ethanol yield of 1.35 mol‐EtOH/mol‐glucose, and with the hydrogen production rate of 6.1 mmol/h/L (H2 yield of 0.80 mol‐H2/mol‐glucose). PCR‐DGGE analysis revealed that the AK17 became the dominant bacterium in the bioreactor. In conclusion, strain AK17 is a promising strain for the co‐production of ethanol and hydrogen with a wide substrate utilization spectrum, relatively high ethanol tolerance, and ethanol yields among the highest reported for thermoanaerobes. Biotechnol. Bioeng. 2008;101: 679–690.

Aerobic fluidized-bed treatment of polychlorinated phenolic wood preservative constituents

Abstract Degradation of polychlorinated phenols was studied in continuous-flow fluidized-bed reactors using pure oxygen for aeration and celite carrier for cell immobilization. High dilution rates and chlorophenols as the only source of carbon and energy were used for maintenance of the mixed biofilm cultures. The chlorophenol degradation performance was monitored as release of inorganic chloride and removal of total organic carbon and by direct gas chromatographic analyses. Continuous polychlorophenol biodegradation activity was maintained in a fluidized-bed reactor for 315 days. Chloride release and chlorophenol removal efficiencies of over 99% were achieved at substrate loading rates of up to 430 g 2,4,6-trichlorophenol/m 1 /d and 400 g 2,3,4,6-tetrachlorophenol/m 1 /d at 3–5 h hydraulic retention times, respectively. Immobilized mixed cultures biodegraded 2,3,4,6-tetrachlorophenol with partial efficiency at feed concentrations as high as 157 mg/l as indicated by inorganic chloride release. Inorganic chloride release in experiments with practical grade 2,3,4,6-tetrachlorophenol exceeded that which is possible by dechlorination of tetrachlorophenol alone suggesting dechlorination of unidentified chlorinated impurities of the preparation as well. Fluidized-bed treatment of simulated wood preservative contaminated groundwater at a chlorophenol loading rate of 217 g/m 1 /d and 5 h hydraulic retention time resulted in the following removal efficiencies: 99.5% for 2,4,6-trichlorophenol, 99.6% for 2,3,4,6-tetrachlorophenol and 92.5% for pentachlorophenol.

High-Efficiency Hydrogen Production by an Anaerobic, Thermophilic Enrichment Culture From an Icelandic Hot Spring

Dark fermentative hydrogen production from glucose by a thermophilic culture (33HL), enriched from an Icelandic hot spring sediment sample, was studied in two continuous‐flow, completely stirred tank reactors (CSTR1, CSTR2) and in one semi‐continuous, anaerobic sequencing batch reactor (ASBR) at 58°C. The 33HL produced H2 yield (HY) of up to 3.2 mol‐H2/mol‐glucose along with acetate in batch assay. In the CSTR1 with 33HL inoculum, H2 production was unstable. In the ASBR, maintained with 33HL, the H2 production enhanced after the addition of 6 mg/L of FeSO4 · 7H2O resulting in HY up to 2.51 mol‐H2/mol‐glucose (H2 production rate (HPR) of 7.85 mmol/h/L). The H2 production increase was associated with an increase in butyrate production. In the CSTR2, with ASBR inoculum and FeSO4 supplementation, stable, high‐rate H2 production was obtained with HPR up to 45.8 mmol/h/L (1.1 L/h/L) and HY of 1.54 mol‐H2/mol‐glucose. The 33HL batch enrichment was dominated by bacterial strains closely affiliated with Thermobrachium celere (99.8–100%). T. celere affiliated strains, however, did not thrive in the three open system bioreactors. Instead, Thermoanaerobacterium aotearoense (98.5–99.6%) affiliated strains, producing H2 along with butyrate and acetate, dominated the reactor cultures. This culture had higher H2 production efficiency (HY and specific HPR) than reported for mesophilic mixed cultures. Further, the thermophilic culture readily formed granules in CSTR and ASBR systems. In summary, the thermophilic culture as characterized by high H2 production efficiency and ready granulation is considered very promising for H2 fermentation from carbohydrates. Biotechnol. Bioeng. 2008;101: 665–678.