Reza Sharafi - Microbial Biotechnology Department, Agricultural Biotechnology Research Institute (ABRII), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran
Gholamreza Salehi Jouzani - Microbial Biotechnology Department, Agricultural Biotechnology Research Institute (ABRII), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran
Ebrahim Karimi - Microbial Biotechnology Department, Agricultural Biotechnology Research Institute (ABRII), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran
Hossein Ghanavati - Microbial Biotechnology Department, Agricultural Biotechnology Research Institute (ABRII), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran
Mojegan Kowsari - Microbial Biotechnology Department, Agricultural Biotechnology Research Institute (ABRII), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran

The objective of the present study was to optimize fast production of enriched biocompost and humic acidfrom rice straw at lab and pilot level using bioprocess engineering and metagenomics approach. The effectivebacteria and fungi with high hydrolytic activities were isolated and characterized from simulated compostingprocess based on their cellulase, xylanase and amylase activities. The ۱۶SrDNA and ITS sequencing showedthat the selected strains were belonged to Bacillus licheniformis, Nocardiopsis alba, B. subtilis andThermoascus aurantiacus. The effects of different materials, including rice straw (RS), chicken manure (CM),urea, olive waste (OW), zeolite, biochar and two groups of native microbial boosters were assayed using ۸treatments and ۳ replicates at lab level (۹ kg) during ۶۰ days. Carbon/nitrogen ratio, pH, EC, temperature,and macro/micro element contents and humic acid production were measured during the process. Then, twoselected treatments, including K and M (containing RW, CM, OW, zeolite, biochar and microbial booster ۱and ۲ (B. licheniformis, N. alba, B. subtilis and T. aurantiacus or Trichoderma sp, respectively) and thecontrol (RW) were used for the pilot level (۵۰۰ kg). The treatments K and M showed maximum temperatureincrease (up to ۶۷ °C), NPK contents, C/N ratio reduction (۷۲.۱۱ and ۶۵.۰۷ %, respectively) and maximumhumic acid production (۳۱۰ and ۲۶۴ g/kg) compared to the control (۳۶ g /kg). Moreover, the humic acidextracted from the treatment K showed maximum positive effects on wheat growth indexes. Metagenomeanalysis showed that two phyla of Proteobacteria and Firmicutes (with a frequency of ۶۷% and ۲۷%,respectively) were dominant in the treatments K and M during three composting phases, whereas generaSphingobacterium and Pseudomonas were predominant in the control (A). The genus Bacillus was dominantin K and M. Alpha analysis showed that the richness and evenness in the maturation and mesophilic phaseswere greater than in the thermophilic phase. Moreover, the beta analysis revealed that maturation phase inthe treatment M had a similar variety to mesophilic phase in the K. Interestingly, microbiome of the controlwas not significantly changed during the three temperature phases. Based on the functional analysis, themaximum enzymatic activities were observed in the thermophilic phases in K and M. Among the strainsadded to the composting process, T. aurantiacus and B. subtilis had significant effects on the decompositionof lignin and cellulose during the process.

Rice straw, Biocompost, Humic acid, Metagenomics