Kinetic behaviour of waste tyre rubber as microorganism support in an anaerobic digester treating cane molasses distillery slops

The kinetics of anaerobic digestion of cane molasses distillery slops was investigated using a continuous-flow bioreactor which contained waste tyre rubber as support, to which the microorganisms became immobilized. Hydraulic retention times (HRT) ranging from 1 to 10 days were investigated at an average influent chemical oxygen demand (COD) concentration of 47.7?g/l. The maximum substrate utilization rate, k, and half saturation coefficient, K _L, were determined to be 1.82?kg COD_removed/kg VSS day and 0.33?kg COD/kg VSS day. The yield coefficient, Y, and sludge decay rate coefficient, K _d, were also determined to be 0.06?kg VSS/kg COD_removed and 0.05?day^-1, respectively. Methane production was maximum (6.75?l/l day) at a 2 day HRT corresponding to a biomass loading rate of 2.578?kg COD/kg VSS day. Biogas yield ranged between 0.51?l/g COD (HRT=2 days) and 0.25?l/g COD (HRT=1?day). In addition, the methane percentage in the biogas varied between 70.5% (HRT=10?days) and 47.5% (HRT=1?day). The close relationship between biomass loading rate and specific substrate utilization rate supported the use of Monod equations. Finally, the experimental values of effluent substrate concentration were reproduced with deviations equal to or less than 10% in every case.     

Methane production from dairy manure filtrate and supernatants

An anaerobic fixed-film reactor receiving screened dairy manure filtrate and supernatants was operated at 35°C and a hydraulic retention time (HRT) of 1 day. Methane production rates were very similar for both the screened slurry and supernatants. The results indicated that using supernatants from the sedimentation process could simplify the operational procedure in a methane production system. The utilization of a fixed-film reactor in methane production process could accommodate a hydraulically flushed dairy waste treatment system.     

A novel process configuration for anaerobic digestion of source-sorted household waste using hyper-thermophilic post-treatment

A novel reactor configuration was investigated for anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW). An anaerobic hyper-thermophilic (68 degrees C) reactor R68 was implemented as a post-treatment step for the effluent of a thermophilic reactor R1 (55 degrees C) in order to enhance hydrolysis of recalcitrant organic matter, improve sanitation and ease the stripping of ammonia from the reactor. The efficiency of the combined system was studied in terms of methane yield, volatile solids (VS) reduction, and volatile fatty acid (VFA) production at different hydraulic retention times (HRT). A single-stage thermophilic (55 degrees C) reactor R2 was used as control. VS reduction and biogas yield of the combined system was 78-89% and 640-790 mL/g VS, respectively. While the VS reduction in the combined system was up to 7% higher than in the single-stage treatment, no increase in methane yield was observed. Shifting the HRT of the hyper-thermophilic reactor from 5 days to 3 days resulted in a drop in the methanogenic activity in the hydrolysis reactor to a minimum. Operation of R68 at HRTs of 24-48 h was sufficient to achieve high VS conversion into VFAs. Removal of pathogens was enhanced by the hyper-thermophilic post-treatment. 7% of the ammonia load was removed in the hyper-thermophilic reactor with a flow of headspace gas through the reactor equivalent to four times the biogas flow produced in reactor R1.     

Methane production using whole and screened dairy manure in conventional and fixed-film reactors

The technical feasibility of adopting the fixed-film reactor concept for biogas production from screened dairy manure was investigated. The methane production capability of laboratory-scale 4-L anaerobic reactors (conventional and fixed-film) receiving screened dairy manure and operated at 35 degrees C was compared. Dairy manure filtrate with 4.4% total solids (TS) and 3.4% volatile solids (VS) (average value) was prepared from 1:1 manure-water slurry. The feed material was added intermittently at loading rates ranging from 2.34 to 25 and 2.25 to 785 g VS/L d, respectively, for the conventional and fixed-film reactors. Maximum methane production rate (L CH(4)/L d) for the conventional reactor was 0.63 L CH(4)/L d achieved at a 6-day hydraulic retention time (HRT). For the fixed-film reactor the maximum production rate was 3.53 L CH(4)/L d when operated at a loading rate of 262 g VS/L d (3 h HRT). The fixed-film reactor was capable of sustaining a loading of 785 g VS/L d (1 h HRT). The fixed-film reactor performed much better than the conventional reactors. These results indicate that a large reduction of required reactor volume is possible through application of a fixed-film concept combined with a liquid-solid separation pretreatment of dairy manure.     

The effect of different Fe2+ concentrations in culture media on the recycling of ground tyre rubber by Acidithiobacillus ferrooxidans YT-1

Waste rubber has posed challenging environmental and disposal problems across the world. This study focused on the microbial reclaiming of ground tyre rubber (GTR) by Acidithiobacillus ferrooxidans YT-1 cultured in media with variable Fe²⁺ concentrations. The Acidithiobacillus ferrooxidans YT-1 strain with the ability of oxidizing sulfur and reclaiming waste rubber was isolated and identified. Toxicity tests of different rubber and additives in tyre rubber compounds to microorganisms was quantitatively investigated. After desulfurization, there were many small colonies on the surface of the desulfurizated GTR (DGTR), due to surface degradation by A. ferrooxidans YT-1. The amount of small colonies increased and sulfur content decreased with the increase of Fe²⁺ concentrations in the media, implying that Fe²⁺ concentration had a great influence on the degradation ability of A. ferrooxidans YT-1. A medium with a high Fe²⁺ concentration was good for growth of A. ferrooxidans YT-1. Compared with styrene butadiene rubber (SBR)/GTR blends, the tensile strength and elongation at the break of the SBR/DGTR blends were significantly improved. The scanning electron microscope (SEM) photographs of the fracture surface further indicated a good coherency between DGTR and the SBR matrix. These results revealed that A. ferrooxidans YT-1 cultured in a medium with a high Fe²⁺ concentration could improve the reclaiming efficiency of waste rubber.     

Influence of temperature on the performance of anaerobic fixed-film reactors utilizing screened dairy manure

Thermophilic (55°C) and mesophilic (35°C and 22°C) anaerobic digestions in laboratory scale (4 litre) fixed-film reactors fed with screened dairy manure were successfully operated over a range of hydraulic retention times, from 1 to 20 days. Maximum methane production rates of 1·82, 1·68 and 1·28 litres CH₄ litre⁻¹ day⁻¹ occurred at 1, 1·5 and 1 days HRT for the respective 55°C, 35°C and 22°C reactors. Both thermophilic and mesophilic digestions achieved maximum biodegradation efficiency at 10 days HRT. The thermophilic fixed-film reactor performed better than completely-mixed reactors in terms of methane production at HRTs shorter than 2 days. From the results, mesophilic fixed-film reactor operated at 35°C provided optimum methane production and net energy output between 1 and 5 days HRT.     

Effect of mixing on biogas production during mesophilic anaerobic digestion of screened dairy manure in a pilot plant

The effect of mixing on biogas production of a 1.5‐m³ pilot continuous stirred tank reactor (CSTR) processing screened dairy manure was evaluated. Mixing was carried out by recirculation of reactor content with a mono pump. The experiment was conducted at a controlled temperature of 37±1°C and hydraulic retention times (HRTs) of 20 and 10 days. The effect of continuous and intermittent operation of the recirculation pump on biogas production was studied. At 10 days of HRT, the results showed a minimal influence of recirculation rate on biogas production and that continuous recirculation did not improve reactor performance. At 20 days of HRT, the recirculation rate did not affect reactor performance. Combination of low solid content in feed animal slurry and long HRTs results in minimal mixing requirements for anaerobic digestion.     

Polyhydroxyalkanoate production using waste vegetable oil and filtered digestate liquor of chicken manure

Abstract

The production of polyhydroxyalkanoates (PHA) using digestate of chicken manure combined with waste sunflower oil as no-cost feedstocks in a multi-stage process was investigated. Using Cupriavidus necator H16 in combined culture media, a maximum PHA accumulation of 4.6?±?0.2?g/L at 75.1?±?1.4% of cell dry matter and a residual cell matter yield of 1.5?±?0.1?g/L were obtained after 96?hr of cultivation (30?°C, 160?rpm, pH 7.0) in flask-based experiments. Manure was acidogenically fermented in a continuous stirring tank reactor in fed-batch mode. The bioreactor was operated at varying organic loading rates (OLR) and hydraulic retention times (HRT) ranging from 1–4?g volatile solids (VS)/L/d and 4–8?days, respectively. Optimal operation was observed at an OLR of 4?g VS/L/d and an HRT of 4?days. Analysis showed the presence of significant amounts of ammonia, potassium, magnesium, calcium, and trace elements, i.e. Fe, Cu, Ni, Mn, Co, Zn, Cr in the digestate. The micro-filtered digestate was utilized as a complex culture media base while waste oil served as an additional carbon source and supplemented for effective PHA production. The total volatile fatty acid content of digestate greatly affected the growth performance of the PHA-producing microorganism Cupriavidus necator H16.     

Anaerobic organic acid production of food waste in once-a-day feeding and drawing-off bioreactor

Acidogenesis of food waste was studied in a 2-L reactor with semi-continuous mode operation (once-a-day feeding and draw-off) for maximum 65 days to examine optimal volatile acid compositions for biological nitrogen removal (BNR) and enhanced biological phosphorus removal (ENPR). Various operational parameters of hydraulic retention time (HRT), organic loading rate (ORL), pH and temperature were investigated for soluble chemical oxygen demand (SCOD), volatile fatty acid composition, nitrogen and phosphate. The yields (gTVFA/g VS) and the volumetric productivity (gTVFA/d L) increased with HRT from 0.26-0.32, 1.25-1.50 (at 4 days) to 0.36-0.39, 1.71-1.83 (at 12 days). However, the acetate fraction (%) decreased with HRT from 35.7-37.5 at 4 days to 23.5-25 at 12 days. The yields decreased with increase of organic loading from 0.34-0.37 at 5 g/L d to 0.29-0.30 at 13 g/L d and the productivity increased from 1.63-1.65 to 3.61-3.75. The yield and productivity were highest at 35 degrees C among 25, 35 and 45 degrees C. The yield and productivity at pH 5.5 and 6.0 were best and very similar to each other. The condition of 35 degrees C, pH 6.0, HRT 8 days, ORL 9 g/L d resulted in TVFA, SCOD, acetate and butyrate of 25, 39.5, 12 and 5.25 g/L, respectively.     

The role of HRT and low temperature on the acid-phase anaerobic digestion of municipal and industrial wastewaters

Two identical 31 completely mixed reactors with solids recycling capabilities were used to investigate the effects of hydraulic retention time (HRT) and low temperatures on volatile fatty acid (VFA) production. One reactor was fed with a 1:1 ratio of diluted primary sludge and a starch-rich industrial wastewater, while the other was fed with diluted primary sludge alone. The VFA and soluble COD concentrations and specific production rates reached their highest values at 30 h HRT and at 25 degrees C. Further increase in HRT (at 25 degrees C) or decrease in temperature (at an HRT of 30 h) resulted in lower amounts of VFA and COD produced. All parameters related to VFA and COD production were significantly higher in the industrial-municipal reactor than in the municipal-only reactor. The VFA:COD ratios were very high, with values ranging from about 0.8 to 1.0 indicating that hydrolysis was the rate-limiting step. Degradation of proteins (measured by ammonia production) was inhibited by the starch-rich wastewater in the industrial-municipal reactor, while no evidence of inhibition was found in the municipal-only reactor. This study revealed that VFA production was feasible at low temperatures (down to 8 degrees C), particularly in the presence of the industrial waste. Ultimately, the amount VFA produced was adequate, in most cases, to support subsequent biological nutrient removal (BNR) processes.     

Mesophilic biogas production from fruit and vegetable waste in a tubular digester

A semi-continuously mixed mesophilic tubular anaerobic digester was tested for the conversion of fruit and vegetable waste (FVW) into biogas. The effect of hydraulic retention time (HRT) and the feed concentration on the extent of the degradation of the waste was examined. Varying the HRT between 12 and 20 days had no effect on the fermentation stability and pH remained between 6.8 and 7.6, but an inhibition of methanogenic bacteria was observed at HRT below 12 days. The overall performance of the reactor was depressed by changing the feed concentration from 8% to 10% TS (dry weight). By applying a feed concentration of 6% and HRT of 20 days in the tubular digester, 75% conversion efficiency of FVW into biogas with a methane content of 64% was achieved.     

Flocculants effect in biomass retention in a UASB reactor treating dairy manure

The performance and biomass retention of an upflow anaerobic sludge bed (UASB) reactor treating liquid fraction of dairy manure has been investigated at several organic loading rates. Two identical UASB reactors were employed. The biomass of one UASB reactor (FBR) had previously been treated with a cationic polyacrylamide, the other reactor was operated as a control reactor (CR). At 3 and 2 days of HRT both reactors functioned similarly, but at 1.5 days HRT some differences were observed between both effluents. Mean COD(T) removal percentages were 83.4% and 76.5%; COD(VFA) values in effluents were 977 and 2682 mg l(-1) for the FBR and the CR respectively. The VSS initial value in both reactors was 25.66 g VSS, whereas after the experiment the quantities were 31.83 g VSS in the FBR and 23.18 g VSS in the CR reactors. Polymer addition resulted in a higher degree of biomass retention and better performance in the FBR reactor.     

Biological hydrogen production by immobilized cells of Clostridium tyrobutyricum JM1 isolated from a food waste treatment process

A fermentative hydrogen-producing bacterium, Clostridium tyrobutyricum JM1, was isolated from a food waste treating process using 16S rRNA gene sequencing and amplified ribosomal DNA restriction analysis (ARDRA). A fixed-bed bioreactor packed with polyurethane foam as support matrix for the growth of the isolate was operated at different hydraulic retention time (HRT) to evaluate its performance for hydrogen production. The reactor achieved the maximal hydrogen production rate of 7.2 l H(2)l(-1)d(-1) at 2h HRT, where hydrogen content in biogas was 50.0%, and substrate conversion efficiency was 97.4%. The maximum hydrogen yield was 223 ml (g-hexose)(-1) with an influent glucose concentration of 5 g l(-1). Therefore, the immobilized reactor using C. tyrobutyricum JM1 was an effective and stable system for continuous hydrogen production.     

Anaerobic digestion of animal waste: waste strength versus impact of mixing

We studied the effect of mode of mixing (biogas recirculation, impeller mixing, and slurry recirculation) and waste strength on the performance of laboratory scale digesters. The digesters were fed with 5% and 10% manure slurry, at a constant energy supply per unit volume (8 W/m3). The experiments were conducted in eight laboratory scale digesters, each having a working volume of 3.73 L, at a controlled temperature of 35+/-2 degrees C. Hydraulic retention time (HRT) was kept constant at 16.2 days, resulting in a total solids (TS) loading rate of 3.08 g/Ld and 6.2 g/Ld for 5% and 10% manure slurry feeds, respectively. Results showed that the unmixed and mixed digesters performed quite similarly when fed with 5% manure slurry and produced biogas at a rate of 0.84-0.94 L/Ld with a methane yield of 0.26-0.31 L CH4/g volatile solids (VS) loaded. This was possibly because of the low solids concentration in the case of 5% manure slurry, where mixing created by the naturally produced gas might be sufficient to provide adequate mixing. However, the effect of mixing and the mode of mixing became prominent in the case of the digesters fed with thicker manure slurry (10%). Digesters fed with 10% manure slurry and mixed by slurry recirculation, impeller, and biogas recirculation produced approximately 29%, 22% and 15% more biogas than unmixed digester, respectively. Deposition of solids inside the digesters was not observed in the case of 5% manure slurry, but it became significant in the case of 10% manure slurry. Therefore, mixing issue becomes more critical with thicker manure slurry.     

Effect of low pH start-up on continuous mixed-culture lactic acid fermentation of dairy effluent

Mixed-culture fermentation that does not require an energy-intensive sterilization process is a viable approach for the economically feasible production of lactic acid (LA) due to the potential use of organic waste as feedstock. This study investigated mixed-culture LA fermentation of whey, a high-strength organic wastewater, in continuous mode. Variations in the hydraulic retention time (HRT) from 120 to 8 h under different pH regimes in two thermophilic reactors (55 °C) were compared for their fermentation performance. One reactor was maintained at a low pH (pH 3.0) during operation at HRTs of 120 to 24 h and then adjusted to pH 5.5 in the later phases of fermentation at HRTs of 24 to 8 h (R1), while the second reactor was maintained at pH 5.5 throughout the experiment (R2). Although the LA production in R1 was negligible at low pH, it increased dramatically after the pH was raised to 5.5 and exceeded that in R2 when stabilized at HRTs of 8 and 12 h. The maximum yield (0.62 g LA/g substrate fed as the chemical oxygen demand (COD) equivalent), the production rate (11.5 g/L day), and the selectivity (95 %) of LA were all determined at a 12-h HRT in R1. Additionally, molecular and statistical analyses revealed that changes in the HRT and the pH significantly affected the bacterial community structure and thus the fermentation characteristics of the experimental reactors. Bacillus coagulans was likely the predominant LA producer in both reactors. The overall results suggest that low pH start-up has a positive effect on yield and selectivity in mixed-culture LA fermentation.     

Two-stage anaerobic fermentation of organic waste in CSTR and UFAF-reactors.

The mechanically separated liquid fraction of organic waste from households was used as a substrate for anaerobic fermentation. A two-step system consisting of a 2001 continuously stirred tank reactor (CSTR) and a 501 upflow anaerobic filter filled with glass foam pearls was constructed. The CSTR was operated for 5 months with a loading rate of 9.8 kg CSB m(-3) day(-1). At a resulting hydraulic retention time (HRT) of 24 days, 68% COD was degraded and a gas productivity of 4.0 m3 m(-3) day(-1) was achieved. Further digestion of the CSTR output was separately optimised in a 20 l-UFAF and based on these results a 50 l-UFAF was connected to the CSTR. At a resulting hydraulic retention time (HRT) of 6 days 38% COD was degraded and a gas productivity of 1.8 m3 m(-3) day(-1) was achieved with the 50 l-UFAF. Thus, the overall degradation efficiency of the two-phase system was 80%. The methane content (61%) of the biogas produced in the 50 l-UF     

Anaerobic Digestion of Dairy Manure in a Hybrid Reactor with Biogas Recirculation

Summary A novel anaerobic hybrid reactor (AHR) configuration incorporating floating support media for biomass immobilization and biogas recirculation for enhanced mixing was used for anaerobic digestion of dairy manure. No pretreatment or solid liquid separation was applied. The reactor was operated at high influent volatile solids (VS) and organic loading rates (OLR) of up to 9.87% and 7.30 g VS/l day, respectively. After 149 days of continuous operation the results revealed that a high amount (38.1 g VSS) of biomass was able to attach itself to the support medium being used. The investigated AHR configuration achieved COD, BOD, TS, and VS removal efficiencies of 48–63, 64–78, 55–65, and 59–68%, respectively, at a hydraulic retention time (HRT) of 15 days. The corresponding average methane production value obtained in this study was 0.191 l/g VS added.     

Aerobic treatment of dairy wastewater with sequencing batch reactor systems

Performances of single-stage and two-stage sequencing batch reactor (SBR) systems were investigated for treating dairy wastewater. A single-stage SBR system was tested with 10,000 mg/l chemical oxygen demand (COD) influent at three hydraulic retention times (HRTs) of 1, 2, and 3 days and 20,000 mg/l COD influent at four HRTs of 1, 2, 3, and 4 days. A 1-day HRT was found sufficient for treating 10,000-mg/l COD wastewater, with the removal efficiency of 80.2% COD, 63.4% total solids, 66.2% volatile solids, 75% total Kjeldahl nitrogen, and 38.3% total nitrogen from the liquid effluent. Two-day HRT was believed sufficient for treating 20,000-mg/l COD dairy wastewater if complete ammonia oxidation is not desired. However, 4-day HRT needs to be used for achieving complete ammonia oxidation. A two-stage system consisting of an SBR and a complete-mix biofilm reactor was capable of achieving complete ammonia oxidation and comparable carbon, solids, and nitrogen removal while using at least 1/3 less HRT as compared to the single SBR system.     

Microbial degradation of tyre rubber particles

Degradation of rubber particles from tyre treads, having diameters from 0.8 to 2.3 mm, was achieved using Nocardia sp. 835A-Rc, a mutant strain with strong rubber-degrading ability. The entire surface of the particles was uniformly attacked by the organism either without stirring of the culture medium or at a very low stirring rate of 40 rpm. At a higher rate of stirring, however, a small number of large microbial colonies were formed on the rubber surface and separate deep semi-spherical cavities were observed after the removal of microbial cells by washing. The number of microbial colonies decreased with increasing stirring rate but each one of the colonies became larger at the same time. As the result of these two counteracting effects of stirring on microbial activity, the weight loss of the particles increased when the stirring rate was raised from 0 to 40 rpm but decreased when the rate was increased from 40 to 70 or 150 rpm. At the stirring rate of 40 rpm, the weight losses of the particles with mean diameters of about 0.8, 1.1 and 2.3 mm were 57, 50 and 36%, respectively, after 8 weeks. The rate of microbial degradation increased again when the stirring was raised from 150 to 300 rpm.     

Co-digestion of cow manure,food waste and intermittent input of fat

Pulses of oil were added to completely mixed reactors fed with dairy cow manure and food waste, after achieving a stable performance at an organic loading rate of 4.6 ± 0.1 gCOD/(l_reactor day), an oily waste effluent from a canned fish processing industry was fed in the form of pulses. The oil concentration rose up to 9, 12, 15 and 18 gCOD_oil/l_reactor, after the pulse feeding in the reactor. The highest fat concentration of 18 gCOD_oil/l_reactor promoted a persistent inhibition in the process of the continuous reactor, although in batch assays, the reactor content evidenced a capacity to degrade more oil and to degrade the accumulated organic matter. All the other pulses had a positive effect in the methane production. From a practical point of view, this work demonstrates that controlled intermittent inputs of oil can enhance the methane production in a co-digestion of cow manure and food waste.