Characteristics of humic-like acid of Aphodius-processed cow manure and natural cow manure compost

With further increase in aquaculture industry, it is predicted that annually total emissions of livestock feces will reach 42.44 billion tons by 2020. The pollution problems of livestock and poultry feces have become an increasing concern in the international community. It has therefore become imperative to recycle use of livestock and poultry feces. Currently, research has focused mainly on earthworm-processed animal manure and sporadic reports on Aphodius sp. There have also been studies on community species, mouthparts, and morphological and gut characteristics of Aphodius sp. Although intensive studies have been conducted on the structural characteristics of soil humus, humic-like acid has received little focus. The carbon, nitrogen dynamics and humus characteristics of adding decomposed cow dung and Aphodius larval composting have been reported in previous study. However, little has been done on the characteristics of humic-like acid of Aphodius-processed cow-manure (APCM) and natural cow manure compost. To understand cow manure utilization and develop basic data for structural characterization, humic-like acids from two different inorganic extractions were characterized in elemental analyzer, infrared spectrometer and differential thermal analyzer. The humic-like acid samples were extracted from APCM and natural cow manure compost with 0.1 mol·L^-1 NaOH and 0.1 mol·L^-1 Na₄P₂O₇, respectively. Elemental analysis showed that the aromaticity of humic-like acid (Na₄P₂O₇-extracted, NaHLA) from APCM was lower than that from fresh cow manure and natural cow manure compost. The C and N contents of humic-like acid (NaOH-extracted, PAHLA) from APCM were higher than those from fresh cow manure and natural cow manure compost. Also the aromaticity of natural cow manure compost was lower than those of fresh cow manure and APCM. In terms of NaHLA of natural cow manure compost, infrared spectrometry suggested that larger carboxylic acid lipid compounds, ketone compounds, aliphatic compounds and carbohydrates existed in NaHLA of APCM. The carbohydrates, aliphatic compounds, phenolic compounds and cellulose esters of PAHLA from APCM and natural cow manure compost were higher than those from fresh cow manure. Amide compounds of PAHLA from APCM were absorbed in Aphodius digestive process. Thermal analysis suggested that NaHLA from natural cow manure compost had larger thermal stability than that from fresh cow manure and APCM. The aliphatic compound, peripheral functional groups and intra-molecular aromatic structures of NaHLA from APCM were higher than those from fresh cow manure and natural cow manure compost. However, the molecular structure of NaHLA from APCM was of higher complexity than that of NaHLA. PAHLA from APCM had two exotherm peaks whereas mid-temperature exotherm peak disappeared in fresh cow manure and natural cow manure compost. In summary, some differences existed in humic-like acid characteristics from APCM and natural cow manure compost.