Measurement and analysis of biogas fertilizer use efficiency, nutrient distribution and influencing factors of biogas residues and slurry on pig farms

Although the effects of biogas residues and slurry returning to farmland are good,they still cannot be used widely in China.In this study,the biogas fertilizer use efficiency,nutrient distribution and influencing factors of fertilizer use efficiency of biogas residues and slurry in 20 biogas projects in Chongming County,Shanghai,China were measured and analyzed.The correlation and a linear regression fit of parts of test indicators were also analyzed.The results show that pig farm biogas residues and slurry mixture are nutrient-rich and can be used as a high-quality organic fertilizer,while its fertilizer use efficiency is unstable because of the differences among area,raw materials,fermentation technology and operation management.Nutrients are not evenly distributed in biogas residues and slurry.Higher levels of organic matters,P and trace elements were detected in biogas residues and higher levels of water-soluble N and K were detected in biogas slurry.The correlations between some test indicators of biogas residues and slurry mixture are significant,especially between total K and conductivity.Linear regression model fitting results of parts of test indicators are satisfactory.Hence,the values of the other test indicators can be estimated by one known indicator which can effectively reduce the determination workload under some limited situations.

Distribution of heavy metals in pig farm biogas residues and the safety and feasibility assessment of biogas fertilizer

The presence of high levels of heavy metals in anaerobic fermentation residues is a major obstacle to the resource utilization and urgent research for removal of heavy metals in the biogas slurry is needed.The handling of large-scale residue slurry and safely returning to field urgently needed constructive suggestion.The contents of heavy metal elements in the residue of anaerobic digestion processes of the wastewater and waste of the piggery were mainly investigated.The contents of heavy metals in the original fluid and the centrifugal solution were determined in this study.They included elements,such as Cu,Zn,Cr,Cd,Pb,As,Ni,Mn,and Se,which were compared with the existing standard including the irrigation water quality standards(GB5084-2005),comprehensive discharge standard of sewage(GB8978-1996)and water-solubility humic acid fertilizer quality standards(NY1106-2010).The preliminary data suggested that both the heavy metals before and after centrifugation were in excess of the standards to some degree and the exceeding standard rate declined significantly after centrifugation.The absolute contents of heavy metals after centrifugation declined significantly compared with that before centrifugation.Those ratios are 91.8%,73.2%,47.6%,94.5%,93.5%,59.4%,95.8%,100%for Zn,As,Cd,Cr,Cu,Ni,Mn,Pb,respectively.A descriptive statistics as well as a correlational analysis showed that there existed strong correlation among Cu,Pb,and the total suspended solids(TS).Meanwhile,significant correlation was found among TS,Cd,Zn,As,Cr,Ni,and Mn at 0.01 level.The data and the analysis above provided the theoretical and experimental support for the removal of heavy mental mainly characterized by the removal of TS.According to the comparison between contents of heavy mental conversed from large amount nutrients and corresponding standard(NY1110-2006),only as was found beyond standard.It was feasible to apply biogas residues after centrifugation as water-solubility fertilizer due to the fact that As had low accumulation efficiency in soil and plants.

Effect of two biogas residues' application on copper and zinc fractionation and release in different soils

Biogas residue （BR） is widely used as a new green fertilizer in agriculture in China. However, it often contains a high concentration of heavy metals so its application should cause our concern. An incubation experiment was conducted to study the risk of pig biogas residue （PBR） and chicken biogas residue （CBR） application on Liuminying soil （LS） and Yixing soil （YS）. The soils were incubated for one, three and six months with 0, 2%, 4% and 6% addition of BRs. According to BCR extraction results, the PBR and CBR applications induced an increase in the concentration of exchangeable fraction of Zn. As for the concentration of exchangeable fraction of Cu, an increase was only observed in the treatments with PBR application. The heavy metal binding intensity also showed a similar trend. With the PBR application, for the LS and YS, the highest concentrations of exchangeable Zn increased 3.6 and 9.5 times, respectively, while the exchangeable Cu was increased by 52.6% and 187.1%. Dissolved organic carbon was the limiting factor for the exchangeable Cu while the exchangeable Zn was controlled by soil pH. PBR presented more agricultural risk than CBR when used as fertilizer. Meanwhile, BRs were more adaptable to LS than YS according to the heavy metal release results.

Biogas residue biochar integrated with phosphate from its ash for the effective recovery of nutrients from piggery biogas slurry

Magnesium ammonium phosphate(MAP)precipitation generally requires an external phosphorus source to increase the recovery of NH_(4)^(+)-N from biogas slurry.However,P-rich piggery biogas residue has been ignored as a phosphorus source.In this study,biogas residue was carbonized into biogas residue biochar(BRC),followed by acid leaching to synthesize functionalized BRC and release PO_(4)^(3−)-P from its ash as the phosphorus source.The effects of different acids on the leaching efficiency and morphological changes of P in BRC were investigated,and NH_(4)^(+)-N and PO_(4)^(3−)-P in the biogas slurry were recovered with functionalized BRC and MAP precipitation.The results showed that oxalic acid-hydrochloric acid mixed acid could leach more than 96%of P in BRC,while weakening the inhibitory effect of Ca^(2+)on MAP precipitation.The BRC was mainly composed of inorganic P,and most nonapatite IP and apatite P(Ca_(3)(PO_(4))2)were leached during acid leaching,with the latter more easily leached.Under optimal recovery conditions,the method had a significant recovery effect on NH_(4)^(+)-N(96.4%)and PO_(4)^(3−)-P(99.3%)in biogas slurry.The recovery of NH_(4)^(+)-N and PO_(4)^(3−)-P by functionalized BRC was mainly through chemical precipitation(forming NH_(4)MgPO_(4)·H_(2)O precipitate)while bonding with-OH,C=O and C-H functional groups.The final recovery product was also a BRC-based slow-release N-P fertilizer rich in struvite.This study solved the disposal problems of P-rich biogas residue and N-rich biogas slurry while providing an innovative technology for the resource utilization of faecal sewage at pig farms.