Co-digestion of food waste and dairy manure in a two-phase digestion system was conducted in laboratory scale. Four influents of R0, R1, R2, and R3 were tested, which were made by mixing food waste with dairy manure at different ratios of 0:1, 1:1, 3:1, and 6:1, respectively. For each influent, three runs of experiments were performed with the same overall hydraulic retention time (HRT) of 13 days but different HRT for acidification (1, 2, and 3 days) and methanogenesis (12, 11, and 10 days) in two-phase digesters. The results showed that the gas production rate (GPR) of co-digestion of food waste with dairy manure was enhanced by 0.8-5.5 times as compared to the digestion with dairy manure alone. Appropriate HRT for acidification was mainly determined by the biodegradability of the substrate digested. Three-, 2-, and 1-day HRT for acidification were found to be optimal for the digestion of R0, R1, and R2/R3, respectively, when overall HRT of 13 days was used. The highest GPR of 3.97 L/L.day was achieved for R3(6:1) in Run 1 (1 + 12 days), therefore, the mixing ratio of 6:1 and HRT of 1 day for acidification were considered to be the optimal ones and thus recommended for co-digestion of food waste and dairy manure. There were close correlations between degradation of organic matters and GPR. The highest VS removal rate was achieved at the same HRT for acidification and mixing ratio of food waste and dairy manure as GPR in the co-digestion. The two-phase digestion system showed good stability, which was mainly attributed to the strong buffering capacity with two-phase system and the high alkalinity from dairy manure when co-digested with food waste.

Kitchen waste (KW), cattle manure (CM), and the mixture of KW and CM were anaerobically digested. The performances of single digestion with KW or CM and of codigestion with KW and CM were investigated and compared. Two loading rates of 10 and 20 g volatile solid (VS) L−1 were used for KW, CM, and their mixture digestion, respectively. NaOH was used as supplementary for KW, and sulfuric acid pretreatment was used for CM to explore the effects of alkalinity and acidification on methane production to verify the roles of codigestion. Scanning electron microscopy (SEM) was used to analyze the structural changes of CM fibers. The results showed that the codigestion of KW and CM increased methane yield by 44% as compared to the single digestion of KW, and the increase could be attributed to the synergistic effect in the codigestion process. A 32% more methane yield was achieved for the KW with NaOH addition than raw KW, which was due to increased alkalinity and buffering capacity. The methane yield and VS reduction for acid-pretreated CM were 116 and 74% higher than raw CM. SEM analysis showed that the structural changes of CM fibers were helpful for methane production. The results showed that codigestion could obtain better and stable performances and might be one of many options for efficient biogas production.

No abstract

This study was conducted to investigate the changes of main compositions and extractives and their effects on biogas yield enhancement. Four NaOH doses (4%, 6%, 8%, and 10%) and four loading rates (35, 50, 65, and 80 g/L) were used. The rice straw was first pretreated by NaOH in solid-state conditions and anaerobically digested. The main compositions and extractives were then analyzed. The results showed that, compared to the untreated rice straw, 3.2%−58.1% more biogas yields were obtained with 4%−10% NaOH-treated rice straws. Hemicellulose, cellulose, and lignin were decomposed by 35.2%−54.2%, 14.2%−16.4%, and 8.0%−44.5%, respectively, for 4%, 6%, 8%, and 10% NaOH-treated rice straws. Considerable fractions of them were converted to relatively readily biodegradable substances, as indicated by increases of 80.3%−173.6% cold-water extractives and 80.4%−152.8% hot-water extractives. Some irresistible substances were removed, as represented by a 30.9%−51.8% decrease of benzene−ethanol extractives. The chemical structures of hot-water and benzene−ethanol extractives were also changed obviously. It was also found that the soluble sugar contents in the 6% NaOH-treated rice straw were twice that of the untreated one. The results specified that NaOH pretreatment was one of efficient methods to enhance biogas production of rice straw, and the changes of main compositions and extractives made important contributions to the enhancement.

No abstract

Based on continuous three-year measurements (from 2004 to 2007) of eddy covariance and related environmental factors, environmental controls on variation in soil respiration (R s ) during non-growing season were explored in a maize agroecosystem in Northeast China. Our results indicated that during non-growing seasons, daily R s was 1.08-4.08 g CO 2 m -2 d -1 , and the lowest occurred in late November. The average R s of non-growing season was 456.06 ± 20.01 g CO 2 m -2 , accounting for 11% of the gross primary production (GPP) of the growing season. Additionally, at monthly scale, the lowest value of R s appeared in January or February. From the beginning to the end of non-growing season, daily R s tended to decrease first, and then increase to the highest. There was a significant quadratic curve relationship between R s and soil temperature at 10 cm depth when soil temperature was more than 0°C (P<0.001), with the explaining ratio of 38%-70%. When soil water content was more than 0.1 m 3 m -3 , soil moisture at 10 cm depth was significantly parabolically correlated with R s (P<0.001), explaining the rate of 18%-60%. Based on all the data of soil temperature of more than 0°C, a better model for R s was established by coupling soil temperature and moisture, which could explain the rate of up to 53%-79%. Meanwhile, the standard error of regression estimation between the values of prediction and observation for R s could reach 2.7%-11.8%. R s in non-growing season can account for 22.4% of R s in growing season, indicating that it plays a critical role in assessing the carbon budget in maize agroecosystem, Northeast China. soil respiration, non-growing season, soil temperature, soil water content, maize Citation:Li R P, Zhou G S, Wang Y. Responses of soil respiration in non-growing seasons to environmental factors in a maize agroecosystem, Northeast China.

No abstract

No abstract