Kazutaka Umetsu

The combined effect of cefazolin and oxytertracycline on biogas production from thermophilic anaerobic digestion of dairy manure

The individual and combined effect of cefazolin (CFZ) and oxytetracycline (OTC) on thermophilic anaerobic digestion (55°C) of dairy manure in batch digesters was investigated. Methane productions from the concentrations tested (30, 60 and 90 mg L(-1)) were compared with no-antibiotic control. CFZ concentrations showed no inhibition (P>0.05) for methane production. The individual OTC and combined CFZ and OTC at concentrations of 30, 60 and 90 mg L(-1) represented 79.1%, 70.3%, 68.6% (P<0.05) and 88.5%, 82.7%, 70.3% (P<0.05) respectively, of the control values. The high CH4 production, optimal pH and VFA data during digestion indicated the process stability and treatment efficiency.

Selective degradation of tetracycline antibiotics present in raw milk by electrochemical method.

The dairy industry disposes of a large volume of waste milk with antibiotic residues, which is a great cause of much concern in soil and water environments. In this study, the electrochemical oxidation of tetracycline antibiotics (TCs) in cows milk was investigated. Milk contains a high concentration of organic matter, and the concentrations of TCs residues are extremely low. The effects of anode materials and electrolytes on the degradation of oxytetracycline (OTC) were investigated. A higher degradation rate for the OTC was attained using the inactive anode or a NaCl electrolyte. It was found that a physically adsorbed oxidant on the surface of the anode and indirect oxidation using electrogenerated hypochlorite could enhance the degradation of OTC in raw milk. The organic components in milk samples affected the removal rate of the OTC. The removal rate constants for the OTC in raw milk were 2.8-7.7 times higher than the chemical oxygen demand values. It was found that electrochemical oxidation could decompose low concentrations of TCs in high concentrations of organic matter solutions selectively. The results indicate that electrochemical oxidation is an effective method for the treatment of TCs in waste milk.

Biohydrogen production from co-digestion of cow manure and waste milk under thermophilic temperature

Biohydrogen production from co-digestion of cow manure (M) and waste milk (WM), milk from mastitis cows treated with cefazolin, was evaluated in a 3×5 factorial design. Organic loading of 20, 40 and 60g volatile solid (VS)L(-1) were tested at temperature of 55°C using M:WM (VS/VS) 70:30, 50:50, 30:70, 10:90 and 0:100. Hydrogen production increased with organic loading and M:WM to a maximum of 59.5mLg(-1) VS fed at 40g VSL(-1) in M:WM 70:30. Butyrate was the main volatile fatty acid (VFA) accumulated in M:WM 50:50, 30:70 and 10:90. Overall reduction of more than 90% of cefazolin resistant bacteria was observed in all the treatments. The reduction was higher at 40 and 60 than 20g VSL(-1) (P<0.05). Inclusion of waste milk enhances hydrogen production from cow manure and could offer added benefit of waste milk treatment and disposal.

Simultaneous removal of organic matter and nitrogen from milking parlor wastewater by a magnetic activated sludge (MAS) process.

The magnetic activated sludge (MAS) process is a modification of the conventional activated sludge process to improve the solid-liquid separation characteristics. It was developed to reduce the production of excess sludge and the time required for the conventional activated sludge process. In this study, actual milking parlor wastewater was treated with a MAS process and no sludge was removed. The effectiveness of continuous aeration and intermittent aeration in removing organic matter and nitrogen were compared. Both processes were highly efficient at removing chemical oxygen demand (COD) (averaged 91% removal) and ammonium nitrogen (NH(4)-N) (averaged 99% removal). In marked contrast to the continuous aeration process, the 30-min aeration/90-min non-aeration cycle of the intermittent aeration process rapidly reduced the nitrate nitrogen (NO(3)-N) concentration to near-zero. This result indicates that NO(3)-N was almost completely denitrified via nitrite nitrogen (NO(2)-N) to nitrogen gas. Removal of organic material and nitrogen can be considered to have occurred simultaneously in the single tank of the MAS process.

The survival of multidrug‐resistant bacteria in thermophilic and mesophilic anaerobic co‐digestion of dairy manure and waste milk

Anaerobic digestion is considered as a promising method to manage animal waste with antibiotic-resistant bacteria. Current research was conducted to investigate the survival of multidrug-resistant bacteria (MDRB) resistant to three groups of antibiotics: (i) cefazolin, neomycin, vancomycin, kanamycin (group 1); (ii) penicillin, oxytetracycline, ampicillin, streptomycin (group 2); and (iii) cefazolin, neomycin, vancomycin, kanamycin, penicillin, oxytetracycline, ampicillin, streptomycin (group 3), in anaerobic digestion of dairy manure and co-digestion of dairy manure and waste milk at 37°C and 55°C for 22 days, respectively. The population densities of three groups of MDRB on peptone, tryptone, yeast and glucose agar plates incubated at 30°C for 7 days before and after digestion showed 100% destruction in both digestates at thermophilic temperature. Overall reduction of more than 90% of three groups of MDRB was observed in mesophilic digestion with no significant differences (P > 0.05) between manure and milk mixture. Co-digestion of dairy manure and waste milk always produced significantly (P < 0.05) higher total gas and methane gas than digestion of manure alone at both temperatures. Gas production in each case was significantly (P < 0.05) higher in thermophilic digestion than in mesophilic digestion. The results demonstrate that thermophilic co-digestion of dairy manure and waste milk offers more benefits in terms of the environment and economy.

The effect of temperature on survival of pathogenic bacteria in biogas plants

The paper deals with the hygienic advantages of sanitation to treat dairy manure in full-scale biogas plants. The slurry samples were collected from two thermophilic biogas plants (55°C) and two mesophilic biogas plants (38°C) in Hokkaido Japan. A detectable number of Coli-aerogenes group and Enterococcus in the slurries after anaerobic digestion (AD) could not be found in either thermophilic biogas plants. However, in both mesophilic biogas plants the viable numbers of Coli-aerogenes group and Enterococcus were detected in the slurries even after anaerobic digestion. The mean decimation reduction time (T(90) ) values of the Coli-aerogenes group and Enterococcus in the slurries during mesophilic digestion were 13.3 days and 16.7 days, respectively.

Distribution and role of Coprothermobacter spp. in anaerobic digesters

The distribution of Coprothermobacter spp. was investigated in seven anaerobic digesters using 16S rRNA gene-based quantitative PCR. The largest number of Coprothermobacter spp. cells was found in a thermophilic anaerobic digester treating dairy cow manure.

High-solids anaerobic mono-digestion of riverbank grass under thermophilic conditions

The purpose of this study was to investigate the potential of high-solids anaerobic mono-digestion of riverbank grass under thermophilic conditions, focusing on the effects of the strength and the amount of inoculum. Ensiled grass was inoculated with three different inocula; inoculum from liquid anaerobic digester (LI), inoculum from dry anaerobic digester (DI), and mixture of LI and DI (MI), at feedstock-to-inoculum ratio (FIR) of 1, 2 and 4. The ensiling process of riverbank grass reduced moisture content (p>0.05), while the hemicellulose content was significantly increased from 30.88% to 35.15% (p<0.05), on dry matter basis. The highest methane production was at an FIR of 2 with MI (167L/kg VSadded), which was significantly higher (p<0.05) than with DI, but not significant compared to LI (p>0.05). At an FIR of 4, digesters inoculated with LI and DI failed to produce methane, whereas 135LCH4/kg VSadded was obtained with MI. The kinetic studies showed that at an FIR of 1 with LI and MI, the inoculum had less of effects on the hydrolysis rate constant (0.269day-1 and 0.245day-1) and methane production (135 versus 149L/kg VSadded); rather, it affected the lag phase. In a thermophilic HS-AD of riverbank grass, the mixture of inoculum with low and high total solids content (TS) helps increase the TS of inoculum and digestion process. An FIR of 2 was deducted to be the limit for a better startup time and higher volumetric productivity of methane.

Effects of handling parameters on hydrogen sulfide emission from stored dairy manure

Hydrogen sulfide (H2S) emission from liquid manure in the process preceding field application is an important issue in fertigation systems. Given that H2S poses a significant health risk, it is important to determine the effects of different handling parameters on H2S emissions to prevent health risks to farmers. In this study, the effects of total solids (TS; 3, 5, 7, 9, and 11%) and mixing speed (100, 200, 300, and 400 rpm), duration (5, 15, 30, and 60 min), and frequency (one, two, three, and four times a day) on H2S emissions from two different dairy manures were investigated. The results indicate that the quantity of sulfur-containing substrate intake determines the potential of dairy manure to emit H2S because manure from cows fed with concentrate-based feed generates higher amounts of H2S than manure from cows fed with forage-based feed. The H2S concentration increased with TS concentration and reached a maximum of 1133 ppm at a TS of 9%; thereafter, it decreased with further increases in TS concentration. H2S emission increased with mixing speed with a peak concentration of 3996 ppm at 400 rpm. A similar trend was observed for mixing duration. However, there were no significant differences between the amounts H2S emitted at different frequencies of mixing (P > 0.05). The results indicate that mixing speed, duration, and TS are the major determinants of the quantity of H2S emitted from dairy manure. Therefore, to prevent health risks associated with H2S emission from dairy manure, it is recommended that the mixing speed and duration should be kept as low as possible, while a TS concentration of above 9% should be applied during the fertigation of dairy manure.

The survival of cefazolin-resistant bacteria in mesophilic co-digestion of dairy manure and waste milk.

The use of cefazolin to treat mastitic cows leads to cefazolin residues in milk and manure. This is responsible for the high occurrence of cefazolin resistant bacteria (CRB) in waste and the environment. Anaerobic digestion is considered to have the potential to reduce antibiotic-resistant bacteria present in waste that results from concentrated animal feeding operations. Thus, the objective of this study was to investigate the survival of CRB and the digester performance in mesophilic co-digestion of dairy manure and waste milk. The experiment was carried out using three digester compositions: 100% slurry (slurry), 50% slurry + 50% manure (manure mixture) and 50% slurry + 45% manure + 5% waste milk (milk mixture) in batch digesters of 1 l with a working volume of 800 ml in triplicate at 37°C for 34 days. The daily biogas production in each digester, and methane (CH4) and carbon dioxide compositions in the gas were determined. The population densities of total culturable bacteria (TCB) and CRB were determined by plate counts on agar media at day 0, 10, 20 and 34 of digestion. Milk mixture produced the highest (P < 0.05) daily and cumulative total and CH4 gas. The maximum percentage reductions of TCB and CRB in manure and milk mixture was observed at day 20, the values being 96.2%, 96.0% and 99.8% and 99.8% respectively. Final volatile fatty acids (VFA) and pH values of the digesters confirmed the digester stability. Based on the findings, mesophilic anaerobic digestion can be considered a potent method to avoid the dissemination of CRB in nature.