Low concentration of zeolite to enhance microalgal growth and ammonium removal efficiency in a membrane photobioreactor

The aim of this work was to study the growth and nutrient removal efficiency of a mixed microalgal culture with and without the addition of low concentrations (0.5, 1, and 5 g L^-1 of total liquid volume in the reactor) of natural zeolite. A control test in which only zeolite was added into a similar membrane photobioreactor was also conducted. The addition of 0.5 g L^-1 zeolite to a continuously-fed membrane photobioreactor increased the microalgal biomass concentration from 0.50 to 0.90-1.17 g particulate organic carbon per L while the average ammonium removal efficiency increased from 14% to 30%. Upon microscopic inspection, microalgal cells were observed growing on the surface of zeolite particles, which indicates that zeolite can support attached microalgal growth. With higher zeolite doses (1 and 5 g L^-1) inside the reactor, however, the breaking apart of added zeolite particles into finer particles dramatically increased solution turbidity, which likely was not beneficial for microalgal growth and ammonium removal due to reduced light penetration. This work shows that low doses of zeolite can be used as microcarriers to enhance microalgal biomass concentration and ammonium removal efficiency, while minimizing zeolite dose would likely reduce the turbidity effects.

Evaluation of methods for enhancing methane oxidation via increased soil air capacity and nutrient content in simulated landfill soil cover

Landfill soil covers and methanotrophs therein have potential to act as final sinks of the greenhouse gas methane (CH₄) generated in landfills, but soil characteristics in landfills might not support methanotrophic activity due to poor soil material selection or mineralisation over time. Hence, our aim was to determine the performance of mineral landfill soil under simulated CH₄ flux and screen methods for elevating the CH₄ elimination capacity (EC) of soil. The methods tested during the column experiment were inorganic fertilisation (nitrate, phosphate, sulphate, copper), decompaction and amelioration of the soil with compost. The addition of compost proved to be the most effective method for increasing the CH₄ EC of soil, increasing from 55 to 189 g m^-2 d^-1 relative to the untreated control soil. This increase could be attributed to increased air capacity, concentration of soil nutrients and number of cultivable methanotrophs. Also, soil water-holding capacity was identified as a more crucial factor for methanotrophic activity than total porosity. Inorganic fertilisation and decompaction induced only a temporary increase in CH₄ EC, likely resulting from the temporary supply of fertiliser to the nutrient-deprived soil. In conclusion, we suggest that compost amelioration (22 w-%) could be useful for restoring CH₄ EC of old landfill covers as an aftercare action to control environmental impacts of closed landfills.

Cultivation of Scenedesmus acuminatus in different liquid digestates from anaerobic digestion of pulp and paper industry biosludge

Different undiluted liquid digestates from mesophilic and thermophilic anaerobic digesters of pulp and paper industry biosludge with and without thermal pretreatment were characterized and utilized for cultivating Scenedesmus acuminatus. Higher S. acuminatus biomass yields were obtained in thermophilic digestates (without and with pretreatment prior to anaerobic digestion (AD): 10.2±2.2 and 10.8±1.2gL^-1, respectively) than in pretreated mesophilic digestates (7.8±0.3gL^-1), likely due to differences in concentration of sulfate, iron, and/or other minor nutrients. S. acuminatus removed over 97.4% of ammonium and 99.9% of phosphate and sulfate from the digestates. Color (74-80%) and soluble COD (29-39%) of the digestates were partially removed. Different AD processes resulted in different methane yields (18-126L CH₄ kg^-1VS), digestate compositions, and microalgal yields. These findings emphasize the importance of optimizing each processing step in wood-based biorefineries and provide information for pulp and paper industry development for enhancing value generation.

Screening biological methods for laboratory scale stabilization of fine fraction from landfill mining

Increasing interest for the landfill mining and the amount of fine fraction (FF) in landfills (40-70% (w/w) of landfill content) mean that sustainable treatment and utilization methods for FF are needed. For this study FF (<20mm) was mined from a municipal solid waste (MSW) landfill operated from 1967 to 1989. FF, which resembles soil, was stabilized in laboratory scale reactors in two phases: first, anaerobically for 101days and second, for 72days using four different methods: anaerobic with the addition of moisture (water) or inoculum (sewage sludge) and aerobic with continuous water washing, with, or without, bulking material. The aim was to evaluate the effect on the stability of mined FF, which has been rarely reported, and to study the quality and quantity of gas and leachate produced during the stabilization experiment. The study showed that aerobic treatment reduced respiration activity (final values 0.9-1.1mgO₂/gTS) and residual methane potential (1.1LCH₄/kgTS) better than anaerobic methods (1.8-2.3mg O₂/g TS and 1.3-2.4L CH₄/kg TS, respectively). Bulking material mixed in FF in one aerobic reactor had no effect on the stability of FF. The benefit of anaerobic treatment was the production of methane, which could be utilized as energy. Even though the inoculum addition increased methane production from FF about 30%, but the methane production was still relatively low (in total 1.5-1.7L CH₄/kg TS). Continuous water washing was essential to remove leachable organic matter and soluble nutrients from FF, while increasing the volume of leachate collected. In the aerobic treatment, nitrogen was oxidized into nitrite and nitrate and then washed out in the leachate. Both anaerobic and aerobic methods could be used for FF stabilization. The use of FF, in landscaping for example, is possible because its nutrient content (4gN/kg TS and 1g P/kg TS) can increase the nutrient content of soil, but this may have limitations due to the possible presence of heavy metal and other contaminants.

The effect of urine storage on antiviral and antibiotic compounds in the liquid phase of source-separated urine

The behaviour of pharmaceuticals related to the human immunodeficiency virus treatment was studied in the liquid phase of source-separated urine during six-month storage at 20°C. Six months is the recommended time for hygienization and use of urine as fertilizer. Compounds were spiked in urine as concentrations calculated to appear in urine. Assays were performed with separate compounds and as therapeutic groups of antivirals, antibiotics and anti-tuberculotics. In addition, urine was amended either with faeces or urease inhibitor. The pharmaceutical concentrations were monitored from filtered samples with solid phase extraction and liquid chromatography. The concentration reductions of the studied compounds as such or with amendments ranged from less than 1% to more than 99% after six-month storage. The reductions without amendments were 41.9-99% for anti-tuberculotics; <52% for antivirals (except with 3TC 75.6%) and <50% for antibiotics. In assays with amendments, the reductions were all <50%. Faeces amendment resulted in similar or lower reduction than without it even though bacterial activity should have increased. The urease inhibitor prevented ureolysis and pH rise but did not affect pharmaceutical removal. In conclusion, removal during storage might not be enough to reduce risks associated with the studied pharmaceuticals, in which case other feasible treatment practises or urine utilization means should be considered.

Characterization of fine fraction mined from two Finnish landfills

A fine fraction (FF) was mined from two Finnish municipal solid waste (MSW) landfills in Kuopio (1- to 10-year-old, referred as new landfill) and Lohja (24- to 40-year-old, referred as old landfill) in order to characterize FF. In Kuopio the FF (<20mm) was on average 45±7% of the content of landfill and in Lohja 58±11%. Sieving showed that 86.5±5.7% of the FF was smaller than 11.2mm and the fraction resembled soil. The total solids (TS) content was 46-82%, being lower in the bottom layers compared to the middle layers. The organic matter content (measured as volatile solids, VS) and the biochemical methane potential (BMP) of FF were lower in the old landfill (VS/TS 12.8±7.1% and BMP 5.8±3.4 m(3)CH4/t TS) than in the new landfill (VS/TS 21.3±4.3% and BMP 14.4±9.9 m(3)CH4/t TS), and both were lower compared with fresh MSW. In the Kuopio landfill materials were also mechanically sieved in the full scale plant in two size fraction <30 mm (VS/TS 31.1% and 32.9 m(3)CH4/t TS) and 30-70 mm (VS/TS 50.8% and BMP 78.5m(3)CH4/t TS). The nitrogen (3.5±2.0 g/kg TS), phosphorus (<1.0-1.5 g/kg TS) and soluble chemical oxygen demand (COD) (2.77±1.77 kg/t TS) contents were low in all samples. Since FF is major fraction of the content of landfill, the characterization of FF is important to find possible methods for using or disposing FF mined from landfills.

Methane oxidation potential of boreal landfill cover materials: The governing factors and enhancement by nutrient manipulation

Methanotrophs inhabiting landfill covers are in a crucial role in mitigating CH4 emissions, but the characteristics of the cover material or ambient temperature do not always enable the maximal CH4 oxidation potential (MOP). This study aimed at identifying the factors governing MOPs of different materials used for constructing biocovers and other cover structures. We also tested whether the activity of methanotrophs could be enhanced at cold temperature (4 and 12°C) by improving the nutrient content (NO3(-), PO4(3-), trace elements) of the cover material. Compost samples from biocovers designed to support CH4 oxidation were exhibiting the highest MOPs (4.16 μmol CH4 g dw(-1) h(-1)), but also the soil samples collected from other cover structures were oxidising CH4 (0.41 μmol CH4 g dw(-1) h(-1)). The best predictors for the MOPs were the NO3(-) content and activity of heterotrophic bacteria at 72.8%, which were higher in the compost samples than in the soil samples. The depletion of NO3(-) from the landfill cover material limiting the activity of methanotrophs could not be confirmed by the nutrient manipulation assay at 4°C as the addition of nitrogen decreased the MOPs from 0.090 μmol CH4 g dw(-1) h(-1) to <0.085 μmol CH4 g dw(-1) h(-1). At 12°C, all nutrient additions reduced the MOPs. The inhibition was believed to result from high ionic concentration caused by nutrient addition. At 4°C, the addition of trace elements increased the MOPs (>0.096 μmol CH4 g dw(-1)h(-1)) suggesting that this was attributable to stimulation of the enzymatic activity of the psychrotolerant methanotrophs.

Stabilization of fine fraction from landfill mining in anaerobic and aerobic laboratory leach bed reactors

Fine fraction (FF, <20 mm) from mined landfill was stabilized in four laboratory-scale leach bed reactors (LBR) over 180 days. The aim was to study feasibility of biotechnological methods to treat FF and if further stabilization of FF is possible. Four different stabilization methods were compared and their effects upon quality of FF were evaluated. Also during the stabilization experiment, leachate quality as well as gas composition and quantity were analyzed. The methods studied included three anaerobic LBRs (one without water addition, one with water addition, and one with leachate recirculation) and one aerobic LBR (with water addition). During the experiment, the most methane was produced in anaerobic LBR without water addition (18.0 L CH4/kg VS), while water addition and leachate recirculation depressed methane production slightly, to 16.1 and 16.4 L CH4/kg VS, respectively. Organic matter was also removed via the leachate and was measured as chemical oxygen demand (COD). Calculated removal of organic matter in gas and leachate was highest in LBR with water addition (59 g COD/kg VS), compared with LBR without water addition or with leachate recirculation (51 g COD/kg VS). Concentrations of COD, ammonium nitrogen and anions in leachate decreased during the experiment, indicating washout mechanism caused by water additions. Aeration increased sulfate and nitrate concentrations in leachate due to oxidized sulfide and ammonium. Molecular weight distributions of leachates showed that all the size categories decreased, especially low molecular weight compounds, which were reduced the most. Aerobic stabilization resulted in the lowest final VS/TS (13.1%), lowest respiration activity (0.9-1.2 mg O2/g TS), and lowest methane production after treatment (0.0-0.8 L CH4/kg VS), with 29% of VS being removed from FF. Anaerobic stabilization methods also reduced organic matter by 9-20% compared with the initial amount. Stabilization reduced the quantity of soluble nitrogen in FF and did not alter concentration of soluble and insoluble phosphorus, and insoluble nitrogen. All four stabilization methods decreased organic matter and thus are possible stabilization methods for FF, but aerobic treatment was the most efficient in this study.

Effects of heat treatment on hydrogen production potential and microbial community of thermophilic compost enrichment cultures

Cellulosic plant and waste materials are potential resources for fermentative hydrogen production. In this study, hydrogen producing, cellulolytic cultures were enriched from compost material at 52, 60 and 70°C. Highest cellulose degradation and highest H(2) yield were 57% and 1.4 mol-H(2) mol-hexose(-1) (2.4 mol-H(2) mol-hexose-degraded(-1)), respectively, obtained at 52°C with the heat-treated (80°C for 20 min) enrichment culture. Heat-treatments as well as the sequential enrichments decreased the diversity of microbial communities. The enrichments contained mainly bacteria from families Thermoanaerobacteriaceae and Clostridiaceae, from which a bacterium closely related to Thermoanaerobium thermosaccharolyticum was mainly responsible for hydrogen production and bacteria closely related to Clostridium cellulosi and Clostridium stercorarium were responsible for cellulose degradation.

Methane oxidation in a boreal climate in an experimental landfill cover composed from mechanically-biologically treated waste

The present study evaluated microbial methane (CH4) oxidation in a boreally located outdoor landfill lysimeter (volume 112 m3, height 3.9 m) filled with mechanically-biologically treated waste (MBT residual) and containing a cover layer made from the same MBT residual. The calculations based on gas emission and pore gas measurements showed that, between April and October 2005, a significant proportion (> 96%) of the methane produced (< 23 l CH4 m(-2) d(-1)) in the lysimeter was oxidized. Methane was oxidized mainly at the depths of 35-75 cm, as indicated by the upward decrease both in the methane concentration and in the methane-to-carbon dioxide ratio in the pore gas. Lower methane oxidation (< 0.8 CH4 m(-2) d(-1); this was < 22% of the methane produced) was observed only during the coldest time of the year (January 2006), apparently due to the fall in temperature at the depths of 25-70 cm (from 9-25 degrees C during April to October to 2-9 degrees C in January). Unexpectedly, the highest methane oxidation potential (MOP) was observed in samples from the top layer where exposure to methane was low. Overall, the results show that MBT residual is a suitable support medium for methane oxidation in landfill covers in field conditions in a boreal climate.

Effects of solid-liquid separation on recovering residual methane and nitrogen from digested dairy cow manure

The feasibility of optimizing methane and nitrogen recovery of samples obtained from farm biogas digester (35 degrees C) and post-storage tank (where digested material is stored for 9-12 months) was studied by separating the materials into different fractions using 2, 1, 0.5 and 0.25 mm sieves. Mass-balances revealed that digested material mainly consists of <0.25 mm (60-69%) and >2 mm (18-27%) fractions, while fractions between 2 and 0.2 mm made the rest. Incubation of solid fractions >0.25 mm of digester material at 35 degrees C resulted in specific methane yields of 0.060-0.085 m(3)kg(-1) volatile solids (VS) during initial 30-50 d and 0.16-0.18 m(3)kg(-1)VS at the end of 340 d incubation. Similarly, fractions >0.25 mm of post-storage tank material produced 0.055-0.092 m(3)kg(-1)VS and 0.13-0.16 m(3)kg(-1)VS of methane after 30-50 d and after 250 d, respectively. Methane yields for fractions <0.25 mm of post-storage tank was 0.03 m(3)kg(-1)VS after 30-50 d and 0.05 m(3)kg(-1)VS after 250 d compared to 0.20 m(3)kg(-1)VS and 0.41 m(3)kg(-1)VS, respectively for the same fraction of digester material. Separation of digested cow manure into solids and liquid fractions to recover methane may be feasible only for post-storage tank material and not for digester material. Nitrogen management would not be feasible with neither material as total nitrogen and ammonium-nitrogen concentrations were equally distributed among the segregated fractions.

Mechanically-biologically treated municipal solid waste as a support medium for microbial methane oxidation to mitigate landfill greenhouse emissions

The residual fraction of mechanically-biologically treated municipal solid waste (MBT residual) was studied in the laboratory to evaluate its suitability and environmental compatibility as a support medium in methane (CH(4)) oxidative biocovers for the mitigation of greenhouse gas emissions from landfills. Two MBT residuals with 5 and 12 months total (aerobic) biological stabilisation times were used in the study. MBT residual appeared to be a favourable medium for CH(4) oxidation as indicated by its area-based CH(4) oxidation rates (12.2-82.3 g CH(4) m(-2) d(-1) at 2-25 degrees C; determined in CH(4)-sparged columns). The CH(4) oxidation potential (determined in batch assays) of the MBT residuals increased during the 124 d column experiment, from <1.6 to a maximum of 104 microg CH(4) g(dw)(-1) h(-1) (dw=dry weight) at 5 degrees C and 578 microg CH(4) g(dw)(-1) h(-1) at 23 degrees C. Nitrous oxide (N(2)O) production in MBT residual (<15 microg N(2)O kg(dw)(-1) d(-1) in the CH(4) oxidative columns) was at the lower end of the range of N(2)O emissions reported for landfills and non-landfill soils, and insignificant as a greenhouse gas source. Also, anaerobic gas production (25.6 l kg(dw)(-1) during 217 d) in batch assays was low, indicating biological stability of the MBT residual. The electrical conductivities (140-250 mS m(-1)), as well as the concentrations of zinc (3.0 mg l(-1)), copper (0.5 mg l(-1)), arsenic (0.3 mg l(-1)), nickel (0.1 mg l(-1)) and lead (0.1 mg l(-1)) in MBT residual eluates from a leaching test (EN-12457-4) with a liquid/solid (L/S) ratio of 10:1, suggest a potential for leachate pollutant emissions which should be considered in plans to utilise MBT residual. In conclusion, the laboratory experiments suggest that MBT residual can be utilised as a support medium for CH(4) oxidation, even at low temperatures, to mitigate greenhouse gas emissions from landfills.

Enumeration of methanotrophic bacteria in the cover soil of an aged municipal landfill

The enumeration of methanotrophic bacteria in the cover soil of an aged municipal landfill was carried out using (1) fluorescent in situ hybridization (FISH) with horseradish peroxidase-labeled oligonucleotide probes and tyramide signal amplification, also known as catalyzed reporter deposition-FISH (CARD-FISH), and (2) most probable number (MPN) method. The number of methanotrophs was determined in cover soil samples collected during April-November 2003 from a point with low CH(4) emission. The number of types I and II methanotrophs obtained by CARD-FISH varied from 15 +/- 2 to 56 +/- 7 x 10(8) cells g(-1) absolute dry mass (adm) of soil and methanotrophs of type I dominated over type II. The average number of methanotrophs throughout the cover soil profile was highest during May-September when the cover soil temperature was above 13 degrees C. Methanotrophs accounted for about 50% of the total bacterial population in the deepest cover soil layer owing to higher availability of substrate (CH(4)). A lower number of methanotrophs (7 x 10(2) to 17 x 10(5) cells g(-1) adm of soil) was determined by the MPN method compared to the CARD-FISH counts, thus confirming previous results that the MPN method is limited to the estimation of the culturable species that can be grown under the incubation conditions used. The number of culturable methanotrophs correlated with the methane-oxidizing activity measured in laboratory assays. In comparison to the incubation-based measurements, the number of methanotrophs determined by CARD-FISH better reflected the actual characteristics of the environment, such as release and uptake of CH(4), temperature, and moisture, and availability of substrates.

Treatment of leachate from MSWI bottom ash landfilling with anaerobic sulphate-reducing process

Removal of sulphate and toxic elements from the leachate of a field landfill lysimeter (112m(3)), containing municipal solid waste incineration (MSWI) bottom ash, was studied. The leachate was treated in two parallel laboratory upflow anaerobic sludge blanket (UASB) reactors without and with ethanol as additional carbon source. With ethanol more than 65% of sulphate was removed, while without ethanol removal was negligible. The treatment removed Ba, Ca, Cu, Mn, Mo, Ni, Pb, Tl, Sb, Se, Sr, and Zn of the studied 35 trace and other elements. The sequential extraction of the reactor sludge at the end of runs confirmed that with a few exceptions (Ba, Ca, and Cu) the main mechanism by which the elements were removed was precipitation as sulphides.

Thermophilic anaerobic digestion of industrial orange waste

Thermophilic anaerobic digestion of industrial orange waste (pulp and peel) with subsequent aerobic post-treatment of the digestate was evaluated. Methane production potential was first determined in batch assays and the effects of operational parameters such as hydraulic retention times (HRT) and organic loading rates (OLR) on process performance were studied through semi-continuous digestion. In batch assays, methane production potential of about 0.49 m(3) kg(-1) volatile solids (VS)(added waste) was achieved. In semi-continuous digestion, loading at 2.8 kgVS m(-3) d(-1) (2.9 kg total solids (TS) m(-3) d(-1)) and HRT of 26 d produced specific methane yields of 0.6 m(3) kg(-1) VS (added waste) (0.63 m(3) kg(-1) VS(added waste)). Operating at a higher OLR of 4.2 kgVS m(-3) d(-1) (4.4 kg TS m(-3) d(-1)) and 40 d HRT produced 0.5 m(3) of methane kg(-1) VS (added waste) (0.63-0.52 m(3) kg(-1) TS (added waste). Up to 70% of TS of industrial orange waste (11.6% TS) was methanised. Further increase in OLR to 5.6 kg VS m(-3) d(-1) (5.9 kg TS m(-3) d(-1); HRT of 20 d) resulted in an unstable and non-functional digester process shown directly through complete cessation of methanogenesis, drop in methane content, reduced pH and increase in volatile fatty acid (VFA) concentrations, especially acetate and soluble chemical oxygen demand. A pH adjustment (from an initial 3.2 to ca. 8) for the low pH orange waste was necessary and was found to be a crucial factor for stable digester operation as the process showed a tendency to be inhibited due to accumulation of VFAs and decrease in digester pH. Aerobic post-treatment of digestate resulted in removal of ammonia and VFAs.

The effects of post-treatments and temperature on recovering the methane potential of >2 mm solid fraction of digested cow manure

The effects of thermal and chemical treatments, mechanical maceration and freezing and thawing on recovering the remaining methane potential of the >2 mm solid fraction of digested cow manure - which accounted for 30% of the original potential of digested cow manure - were studied in laboratory batch assays at 5-20 degrees C and at 35-55 degrees C to evaluate the treatment effects both under long-term (340 d) storage of solids and during active digestion (30 d), respectively. The effects of different treatments on the methane production of the solids varied with incubation temperatures and time. However, in all cases, methane productions at 15 degrees C and lower were slow and low for both untreated and treated solids even after long-term incubation. At 35 and 55 degrees C more methane was recovered from untreated solids producing up to 61-82 ml g(-1) volatile solids (VS)added in 30 d and 179-215 ml g(-1) VSadded in 340 d. Only chemical treatment with or without thermal treatment enhanced the methane yields while some treatments even decreased the yields. An increase in temperature to 35 degrees C of the assays incubated for 6 months at < or =20 degrees C initiated more significant methane production. In conclusion, the methane potential of the digested solids in a farm-scale biogas system can be recovered by active digestion at 35 or 55 degrees C and can be improved to a smaller extent through chemical treatment of separated solids fraction, while methane recovery at lower temperatures and with some of the treatments studied would not be effective.

Hydrolysis rates, methane production and nitrogen solubilisation of grey waste components during anaerobic degradation

Municipal grey waste (i.e. the remaining fraction in municipal waste management systems in which putrescibles (biowaste) and other recyclables (paper, metals, glass) are source-segregated) was manually sorted into six main fractions on the basis of composition and also separated by sieving (100 mm mesh size) into two fractions, oversized and undersized, respectively. In practice, in waste management plant the oversized fraction is (or will be) used to produce refuse-derived fuel and the undersized landfilled after biological stabilisation. The methane yields and nitrogen solubilisation of the grey waste and the different fractions (all studied samples were first milled to 5 mm particle samples) were determined in a 237-day methane production batch assay and in a water elution test, respectively. The grey waste was found to contained remnants of putrescibles and also a high amount of other biodegradable waste, including packaging, cartons and cardboard, newsprint, textiles and diapers. These waste fractions comprised 41%-w/w of the grey waste and produced 40-210 m3 methane (total solids (TS))(-1) and less than 0.01 g NH4-N kg TS(added)(-1) except diapers which produced 9.8 g NH4-N kg TS(added)(-1) in the batch assays. In the case of the two sieved fractions and on mass bases, most of the methane originated from the oversized fraction, whereas most of the NH4-N was solublised from the undersized fraction. The first-order kinetic model described rather well the degradation of each grey waste fraction and component, showing the different components to be in the range 0.021-0.058 d(-1), which was around one-sixth of the values reported for the source-segregated putrescible fraction of MSW.

Anaerobic on-site treatment of black water and dairy parlour wastewater in UASB-septic tanks at low temperatures

Anaerobic on-site treatment of synthetic black water (BW) and dairy parlour wastewater (DPWW) was studied in two-phased upflow anaerobic sludge blanket (UASB)-septic tanks at low temperatures (10-20 degrees C). At all temperatures, total chemical oxygen demand (COD(t)) removal was above 90% with BW and above 80% with DPWW and removal of total suspended solids (TSS) above 90% with both wastewaters. Moreover, dissolved COD (COD(dis)) removal was approx. 70% with both wastewaters indicating good biological activity of the sludges. With BW, a single-phased reactor was found sufficient for good COD removals, while with DPWW, a two-phased process was required. Temperature optimum of reactor sludges was still 35 degrees C after long (398d) operation. Most of the nutrients from BW were removed with TSS, while with DPWW nutrient removal was low. In conclusion, UASB-septic tank was found feasible for (pre)treatment of BW and DPWW at low temperatures.

Removal of bis (2-ethylhexyl) phthalate from reject water in a nitrogen-removing sequencing batch reactor

Reject water from sewage sludge processing may contain high concentrations of nutrients and organic pollutants and cause internal pollution load at a sewage treatment plant (STP) if circulated to the headworks of an STP. In the present study removal of nitrogen and bis (2-ethylhexyl) phthalate (DEHP) from reject water was studied in two sequencing batch reactors (SBRs) with different aerobic/anoxic periods during a 6-h total cycle period. Ammonia-nitrogen (NH(4)-N) was almost totally removed in both reactors, apparently by nitrification throughout the run, while denitrification declined with decreasing SCOD in the influent resulting in an increase in the effluent nitrate-nitrogen (NO(3)-N) concentration. DEHP removals from the water phases were above 95% in both reactors, while the average total removals were 36 and 42%, calculated on a mass basis. Much higher removals occurred in the experiment where one of the systems was spiked with a given amount of DEHP. The spiking experiment suggested that SBRs had the potential to remove DEHP biologically from reject water but that the removal was restricted by the poor bioavailability of DEHP as a result of sorption to solids. This study showed that SBR has the potential to cut the internal load of nitrogen and hydrophobic organic pollutants in cases where reject water is circulated to the headworks of an STP.

Modeling solid waste decomposition

The hydrolysis rate coefficients of sorted municipal waste were evaluated from the biochemical methane potential tests using non-linear regression. A distributed mathematical model of anaerobic digestion of rich (food) and lean (non-food) solid wastes with greatly different rates of polymer hydrolysis/acidogenesis was developed to describe the balance between the rates of hydrolysis/acidogenesis and methanogenesis. The model was calibrated using previously published experimental data [Biores. Technol. 52 (1995) 245] obtained upon various initial food waste loadings. Simulations of one- and two-stage digestion systems were carried out. The results showed that initial spatial separation of food waste and inoculum enhances methane production and waste degradation in a one-stage solid-bed digester at high waste loading. A negative effect of vigorously mixing at high waste loading reported in some papers was discussed. It was hypothesized that the initiation methanogenic centers developing in time and expanding in space under minimal mixing conditions might be a key factor for efficient anaerobic conversion of solid waste into methane.

Removal of DEHP in composting and aeration of sewage sludge

The potential of composting and aeration to remove bis(2-ethylhexyl) phthalate (DEHP) from municipal sewage sludge was studied with two dewatered sludges: raw sludge and anaerobically digested sludge. Composting removed 58% of the DEHP content of the raw sludge and 34% of that of the anaerobically digested sludge during 85 days stabilisation in compost bins. A similar removal for the anaerobically digested sludge was achieved in a rotary drum in 28 days. Less than 1% of DEHP was removed with the compost leachate. Although DEHP removal was greater from raw sludge compost than anaerobically digested sludge compost, the total and volatile solids removals were on the same level in the two composts. In the aeration of raw sludge at 20 degrees C the DEHP removals were 33-41% and 50-62% in 7 and 28 days, respectively. Both composting and aeration are concluded to have the potential to reduce the DEHP contents typically found in sewage sludges to levels acceptable for agricultural use.

Pilot-scale comparison of thermophilic aerobic suspended carrier biofilm process and activated sludge process in pulp and paper mill effluent treatment

Thermophilic aerobic treatment of settled pulp and paper mill effluent was studied under mill premises with two comparative pilot processes; suspended carrier biofilm process (SCBP) and activated sludge process (ASP). Full-scale mesophilic activated sludge process was a reference treatment. During the runs (61 days) hydraulic retention times (HRTs) were kept 13+/-5 h and 16+/-6 h for SCBP and ASP, respectively. Corresponding volumetric loadings rates (VLR) were 2.7+/-0.9 and 2.2+/-1.0 kg CODfilt m(-3)d(-1). Temperatures varied between 46 to 60 degrees C in both processes. Mesophilic ASP was operated with HRT of 36 h, corresponding VLR of 0.7 kg CODfilt m(-3)d(-1). Both SCBP and ASP achieved CODfilt (GF/A filtered) removals up to 85%, while the mesophilic ASP removal was 89+/-2%. NTU values were markedly higher (100-300) in thermophilic effluents than in mesophilic effluent (30). Effluent turbidity was highly dependent on temperature; in batch experiment mesophilic effluent sample had NTU values of 30 and 60 at 35 degrees C and 55 degrees C, respectively. As a conclusion, both thermophilic treatments gave high CODfilt removals, which were close to mesophilic process removal and were achieved with less than half of HRT.

Effects of temperature on post-methanation of digested dairy cow manure in a farm-scale biogas production system

A post-methanation process that could be adopted at farm-scale, operating at temperatures prevailing in farm manure digester post-storage tanks, was evaluated. Digested manure samples from a farm digester (35 degrees C) and post-storage tank (5-10 degrees C) were incubated in parallel batches at 5-20 degrees C and as reference at 35 and 55 degrees C. Specific methane yields (kg(-1) volatile solids (VS)(added waste)) were 0.20-0.26 m3 at 35-55 degrees C and 0.085-0.09 m3 at 10-20 degrees C for digester material (345 days of incubation) and 0.16-0.21 m3 at 35-55 degrees C, 0.053-0.087 kg(-1) VS(added waste) m3 at 15-20 degrees C and 0.026 m3 at 10 degrees C for post-storage tank material (250 days). Both materials produced less than 0.005 m3 at 5 degrees C. However, an increase in temperature to 35 degrees C (40 days) improved methane production in assays pre-incubated at 5-20 degrees C (9 months). These results suggest that the untapped methane potential of the digested manure cannot effectively be recovered at temperatures prevailing in farm digested manure storage tanks during the winter in Northern latitudes. Nevertheless, as ambient temperatures increase during the late spring, an increase in methanogenesis can be expected.

Microbial diversity in a thermophilic aerobic biofilm process: analysis by length heterogeneity PCR (LH-PCR)

A two-stage pilot-scale thermophilic aerobic suspended carrier biofilm process (SCBP) was set up for the on-site treatment of pulp and paper mill whitewater lining. The microbial diversity in this process was analyzed by length heterogeneity analysis of PCR-amplified 16S ribosomal DNA. The primer pair selected for PCR amplification was first evaluated by a computational analysis of fragment lengths in ten main phylogenetical eubacterial groups. The fragment contained the first third of the 16S rRNA gene, which was shown to vary naturally between 465 and 563 bp in length. The length heterogeneity analysis of polymerase chain reaction (LH-PCR) profile of the biomass attached to carrier elements was found to be diverse in both stages of the SCBP. During normal operating conditions, sequences belonging to beta-Proteobacteria, Cytophaga/Flexibacter/Bacteroides group and gamma-Proteobacteria were assigned to the most prominent LH-PCR peak. Samples from the suspended biomass consisted of completely different bacterial populations, which were, however, similar in the serial reactors. The pilot process experienced alkaline shocks, after which Bacillus-like sequences were detected in both the biofilm and suspended biomass. However, when the conditions were reversed, the normal microbial population in the biofilm recovered rapidly without further biomass inoculations. This study shows that LH-PCR is a valuable method for profiling microbial diversity and dynamics in industrial wastewater processes.

Removal of bis(2-ethylhexyl) phthalate at a sewage treatment plant

Bis(2-ethylhexyl) phthalate (DEHP) concentrations were measured at different stages in a full-scale sewage treatment plant (STP) and mass balances were calculated. The DEHP load to treatment process coming from the sewer system and the internal load comprising returned supernatants and filtrate from sludge treatment and excess secondary sludge were at the same level. The DEHP removal efficiency from the water phase at the STP was on average 94% of sewage DEHP, the main removal process being sorption to primary and secondary sludges. On average 29% of DEHP was calculated to be removed in the biological nitrifying-denitrifying activated sludge process, which was much less than expected from laboratory biodegradation studies described in literature. Monoethylhexyl phthalate, the primary biotransformation product of DEHP, was not detected at any treatment stage. Approximately 32% of DEHP in sewage was removed during anaerobic digestion of the sludge, while 32% remained in the digested and dewatered sludge.

Occurrence and removal of organic pollutants in sewages and landfill leachates

Sewages of different composition and the effluents of four sewage treatment plants (STPs), plus sewage sludges were analysed for semivolatile organic priority pollutants. Furthermore, 11 landfill leachates were analysed to evaluate their contribution to sewage pollutants when co-treated. Bis(2-ethylhexyl) phthalate (DEHP) was the pollutant occurring at highest concentrations (up to 122 microg/l) and it was present in all sewages and leachates; concentrations of other phthalates were usually below 17 microg/l. Some polycyclic aromatic hydrocarbons (PAH) (<1 microg/l) and 2,6-dinitrotoluene (< or =5.9 microg/l) were also present in many of the sewages and leachates. Phthalates were present in STP effluents in low concentrations (<8 microg/l), while PAHs were usually not present. DEHP concentrations were at the same level in the sewage consisting of household wastewater and stormwater runoff and the sewages also including industrial discharges and landfill leachates, while PAHs were present in sewages containing industrial discharges. Leachate contribution to the total pollutant load to the STP was less than 1%. Sorption of DEHP to different particle size fractions in sewage was studied by serial membrane filtration. Most of the DEHP (71-84%) was attached to the particles 0.1-41 microm in size, and approximately 10-27% of the DEHP was sorbed on particles larger than 41 microm. Less than 6% of the DEHP was in the fraction below 0.1 microm and readily available for microbial degradation.

Methane and leachate pollutant emission potential from various fractions of municipal solid waste (MSW): effects of source separation and aerobic treatment

The effects of source-separation of putrescibles as well as aerobic pre-treatment and landfill aeration on the pollutant emission potential of methane and leachate pollutants were studied in the fresh (PFMSW) and composted (CPFMSW) source-separated putrescible fraction of municipal solid waste, and in the grey waste, and in lysimeter landfilled grey waste and ten-year-old unsorted MSW from our landfill lysimeter study. After 0, 23 and 51 days, an aerobic lysimeter experiment, an elution test and biochemical methane potential (BMP) test was done on samples. PFMSW had high methane (CH4) potential (410 m(3) CH4 t(-1)TS) as well as a high amount of ammonium-nitrogen (3.6 kg NH4-N) was eluted, whereas CPFMSW produced 41 m(3) CH4 t(-1)TS and 2.0 kg NH4-N t(-1)TS. A high nitrogen elution potential was found in the grey waste (2.1 kg NH4-N t(-1)TS). Aeration for 51 days in lysimeters reduced CH4 potential by more than 68% for the PFMSW and CPFMSW samples, whereas for the lysimeter landfilled grey waste the reduction was 50% indicating the potential of aeration for CH4 emission reduction. The effective separation and biological treatment of the PFMSW are important in reducing the environmental impacts of waste management, especially for minimising the methane potential of MSW fractions.

Biological nitrogen removal from municipal landfill leachate: low-cost nitrification in biofilters and laboratory scale in-situ denitrification

The slow leaching of nitrogen from solid waste in landfills, resulting in high concentrations of ammonia in the landfill leachate, may last for several decades. The removal of nitrogen from leachate is desirable as nitrogen can trigger eutrophication in lakes and rivers. In the present study, a low-cost nitrification-denitrification process was developed to reduce nitrogen load especially in leachates from small landfills. Nitrification was studied in laboratory and on-site pilot aerobic biofilters with waste materials as filter media (crushed brick in upflow filters and bulking agent of compost in a downflow filter) while denitrification was studied in a laboratory anoxic/anaerobic column filled with landfill waste. In the laboratory nitrification filters, start-up of nitrification took less than 3 weeks and over 90% nitrification of leachate (NH4-N between 60 and 170mg N l(-1), COD between 230 and 1,300 mg l(-1)) was obtained with loading rates between 100 and 130 mgNH4-N l(-1) d at 25 degrees C. In an on-site pilot study a level of nitrification of leachate (NH4-N between 160 and 270 mg N l(-1), COD between 1,300 and 1,600 mg l(-1)) above 90% was achieved in a crushed brick biofilter with a loading rate of 50mg NH4-N l(-1) d even at temperatures as low as 5-10 degrees C. Ammonium concentrations in all biofilter effluents were usually below the detection limit. In the denitrification column. denitrification started within 2 weeks and total oxidised nitrogen in nitrified leachate (TON between 50 and 150mg N l(-1)) usually declined below the detection limit at 25 degrees C, whereas some ammonium, probably originating from the landfill waste used in the column, was detected in the effluent. No adverse effect was observed on the methanation of waste in the denitrification column with a loading rate of 3.8 g TON-N/t-TS(waste) d. In conclusion, nitrification in a low-cost biofilter followed by denitrification in a landfill body appears applicable for the removal of nitrogen in landfill leachate in colder climates.

Semi-continuous anaerobic digestion of solid poultry slaughterhouse waste: effect of hydraulic retention time and loading

We studied the effect of hydraulic retention time (HRT) and loading on anaerobic digestion of poultry slaughterhouse wastes, using semi-continuously fed, laboratory-scale digesters at 31 degrees C. The effect on process performance was highly significant: Anaerobic digestion appeared feasible with a loading of up to 0.8 kg volatile solids (VS)/m3 d and an HRT of 50-100 days. The specific methane yield was high, from 0.52 to 0.55 m3/kg VS(added). On the other hand, at a higher loading, in the range from 1.0 to 2.1 kg VS/m3 d, and a shorter HRT, in the range from 25 to 13 days, the process appeared inhibited and/or overloaded, as indicated by the accumulation of volatile fatty acids and long-chain fatty acids and the decline in the methane yield. However, the inhibition was reversible. The nitrogen in the feed, ca. 7.8% of total solids (TS), was organic nitrogen with little ammonia present, whereas in the digested material ammonia accounted for 52-67% (up to 3.8 g/l) of total nitrogen. The TS and VS removals amounted to 76% and 64%, respectively. Our results show that on a continuous basis under the studied conditions and with a loading of up to 0.8 kg VS/m3 d metric ton (wet weight) of the studied waste mixture could yield up to 140 m3 of methane.

Sulphate-reducing laboratory-scale high-rate anaerobic reactors for treatment of metal- and sulphate-containing mine wastewater

Upflow anaerobic sludge blanket (UASB) reactors were used in this study to evaluate the feasibility of the sulphate-reducing, anaerobic high-rate process to treat metal- and sulphate-containing mining wastewater (MWW). Four simultaneous reactors, inoculated with different inocula (mesophilic granular sludge from two UASB reactors, one treating sugar refinery wastewater and the other board mill wastewater) and operated with different loadings, were for 95 days fed with synthetic feed consisting of glucose and sulphate. In all reactors, 23-72% of sulphate and 12-93% of COD were removed. Subsequently, two reactors were fed with diluted MWW (zinc as the main metal) for 77 days with hydraulic retention times down to 8 hours. At the onset of the runs (until day 48), over 99.9% of zinc was removed in both reactors, after which removals fell to less than 30-80%. At the end of the runs, the highest zinc content (44 mg g(-1) TS) in the reactor sludges was 21 times higher than that in the inoculum. It cannot be concluded definitively that sulphide precipitation was the only mechanism of metal removal, for biosorption may have had a role to play in the process.

Screening of physical-chemical methods for removal of organic material, nitrogen and toxicity from low strength landfill leachates

Physical-chemical methods have been suggested for the treatment of low strength municipal landfill leachates. Therefore, applicability of nanofiltration and air stripping were screened in laboratory-scale for the removal of organic matter, ammonia, and toxicity from low strength leachates (NH4-N 74-220 mg/l, chemical oxygen demand (COD) 190-920 mg O2/l, EC50 = 2-17% for Raphidocelis subcapitata). Ozonation was studied as well, but with the emphasis on enhancing biodegradability of leachates. Nanofiltration (25 degrees C) removed 52-66% of COD and 27-50% of ammonia, the latter indicating that ammonia may in part have been present as ammonium salt complexes. Biological pretreatment enhanced the overall COD removal. Air stripping (24 h at pH 11) resulted in 89% and 64% ammonia removal at 20 and 6 degrees C, respectively, the stripping rate remaining below 10 mg N/l h. COD removals of 4-21% were obtained in stripping. Ozonation (20 degrees C) increased the concentration of rapidly biodegradable COD (RBCOD), but the proportion of RBCOD of total COD was still below 20% indicating poor biological treatability. The effect of the different treatments on leachate toxicity was assessed with the Daphnia acute toxicity test (Daphnia magna) and algal growth inhibition test (Raphidcocelis subcapitata). None of the methods was effective in toxicity removal. By way of comparison, treatment in a full-scale biological plant decreased leachate toxicity to half of the initial value. Although leachate toxicity significantly correlated with COD and ammonia in untreated and treated leachate, in some stripping and ozonation experiments toxicity was increased in spite of COD and ammonia removals.

Aerobic moving bed biofilm reactor treating thermomechanical pulping whitewater under thermophilic conditions

The continuously operated laboratory scale Kaldnes moving bed biofilm reactor (MBBR) was used for thermophilic (55 degrees C) aerobic treatment of TMP whitewater. In the MBBR, the biomass is grown on carrier elements that move along with the water in the reactor. Inoculation with mesophilic activated sludge gave 60-65% SCOD removal from the first day onwards. During the 107 days of experiment, the 60-65% SCOD removals were achieved at organic loading rates of 2.5-3.5 kg SCODm(-3) d(-1), the highest loading rates applied during the run and HRT of 13-22h. Carbohydrates, which contributed to 50-60% of the influent SCOD. were removed by 90-95%, while less than 15% of the lignin-like material (30-35% of SCODin) was removed. The sludge yield was 0.23g VSSg SCOD(-1)removed. The results show that the aerobic biofilm process can be successfully operated under thermophilic conditions.

Simplified hydrolysis models for the optimal design of two-stage anaerobic digestion

This note shows that Contois kinetics, when used to describe the hydrolysis of biodegradable solids, are preferable to the traditional first-order kinetics when considering the optimal design of a steady-state two-stage anaerobic digester system.

Evaluation of kinetic coefficients using integrated monod and haldane models for low-temperature acetoclastic methanogenesis

The integrated Monod and Haldane models were used to evaluate the kinetic coefficients and their standard deviations using the methane accumulation curves of low-temperature acetoclastic methanogenesis. The linear and exponential approximations and the limitations of their applicability were deduced from the integrated models. The samples of lake sediments and biomass taken from a low-temperature upflow anaerobic sludge blanket (UASB) reactor were used as inoculum in batch assays for acetate methanation. In comparison, the Monod and Haldane models were applied to evaluate the kinetic coefficients for mesophilic acetoclastic methanogenesis accomplished by the pure culture of Methanosarcina barkeri strain MS. The Monod and Haldane models and their approximations were fitted by using non-linear regression. For the wide range of initial acetateconcentrations (4.2-84 mM: 5-100 mM) applied to the UASB biomass at 11 and 22 degrees C and for the lake sediment samples at 6 and 15 degrees C, a better fit was obtained with the Haldane models and their exponential approximations, respectively. For the lake sediments the values of inhibition coefficients decreased at decreasing temperatures. At the highest temperature of 30 degrees C no difference was found between the Haldane and Monod models and the simpler Monod model should be preferred. The values of the maximum growth rate of biomass were highest at 30 degrees C (lake sediment) and 22 degrees C (the UASB biomass) being in a range presented in the literature for mesophilic acetoclastic methanogenesis.

Thermophilic anaerobic treatment of sulphur rich forest industry wastewater

Thermophilic anaerobic treatment of sulphur-rich paper mill wastewater (0.8-3.1 gCOD/1, 340-850 mgSO4/l; COD:SO4 3.4-5.3) was studied in three laboratory-scale, upflow anaerobic sludge blanket (UASB) reactors and in bioassays. The reactors were inoculated with non-adapted thermophilic granular sludge. In the bioassays, no inhibition of the inoculum was detected and about 62% COD removal (sulphide stripped) was obtained. About 70 to 80% of the removed COD was methanised. In the reactors, up to 60-74% COD removal (effluent sulphide stripped) was obtained at loading rates up to 10-30 kgCOD/m3d and hydraulic retention times down to 6 to 2 hours. The effluent total sulphide was up to 150-250 mg/l. Sulphide inhibition could not be confirmed from the reactor performances. The results from bioassays suggested that both the inoculum and sludge from the UASB reactor used acetate mainly for methane production, while sulphide was produced from hydrogen or its precursors.

The effect of low temperature (5-29 degrees C) and adaptation on the methanogenic activity of biomass

The influence of low temperature (5-29 degrees C) on the methanogenic activity of non-adapted digested sewage sludge and on temperature/leachate-adapted biomass was assayed by using municipal landfill leachate, intermediates of anaerobic degradation (propionate) and methane precursors (acetate, H2/CO2) as substrates. The temperature dependence of methanogenic activity could be described by Arrhenius-derived models. However, both substrate and adaptation affected the temperature dependence. The adaptation of biomass in a leachate-fed upflow anaerobic sludge-blanket reactor at approximately 20 degrees C for 4 months resulted in a sevenfold and fivefold increase of methanogenic activity at 11 degrees C and 22 degrees C respectively. Both acetate and H2/CO2 were methanized even at 5 degrees C. At 22 degrees C, methanogenic activities (acetate 4.8-84 mM) were 1.6-5.2 times higher than those at 11 degrees C. The half-velocity constant (Ks) of acetate utilization at 11 degrees C was one-third of that at 22 degrees C while a similar Ki was obtained at both temperatures. With propionate (1.1-5.5 mM) as substrate, methanogenic activities at 11 degrees C were half those at 22 degrees C. Furthermore, the residual concentration of the substrates was not dependent on temperature. The results suggest that the adaptation of biomass enables the achievement of a high treatment capacity in the anaerobic process even under psychrophilic conditions.

Acetate treatment in 70 degrees C upflow anaerobic sludge-blanket (UASB) reactors: start-up with thermophilic inocula and the kinetics of the UASB sludges

This study focused on the use the thermophilic anaerobic granulae in the start-up of 70 degrees C acetate-fed upflow anaerobic sludge-blanket (UASB) reactors and the kinetics of granulae grown at 70 degrees C. In the UASB reactors, chemical oxygen demand removal commenced within 48 h of the start-up. The maximum reduction in chemical oxygen demand was 84% with the feed containing yeast and 71% without a yeast supplement. In the bioassays, the yeast-grown sludge converted 98% of the acetate consumed to methane as compared to 92% for the sludge grown without yeast. The highest initial specific methane production rate (mu-CH4) of the UASB sludges grown at 70 degrees C was 0.088 h(-1) at an acetate concentration of 4.6mM. The higher initial acetate concentration was found to prolong the lag-phase in methane production significantly and to decrease mu-CH4. The half-saturation constant (Ks), the inhibition constant (Ki), the inhibition response coefficient (n) and the mu-CH4-max, calculated according to a modified Haldane equation, were 1.5 mM, 2.8 mM, 0.8 and 0.28 h(-1), respectively. The prolonged starvation of the 70 degrees C sludge (15 days) decreased the mu-CH4 from about 0.022 h(-1) to 0.011 h(-1) and increased the lag phase in methane production from 6 h to 24 h as compared with non-starved sludge.