# Digestate Management and Processing Practices: A Review
## 5 Digestate Processing
### Treatments of the Solid Fraction
#### 5.2.1 Composting
15 Lh\({}^{-1}\) kg OM\({}_{0}\) & [94] \\ \hline DG & Concentrations Concentrations Concentrations of OS in DG: 0, 10, 20 and 30; C/N ratio: 25–30; aeration rate: 0.15 Lmin\({}^{-1}\) kg\({}^{-1}\) TS & Influence of OS as BA on compost quality. & Improved OM degradation promoted the transformation of NH\({}_{4}\)+N to NH\({}_{3}\)–N and enhanced compos quality. & [104] \\ \hline Solid residue DG & Concentrations Concentrations Concentrations of OS in DG: 0, 10, 20 and 30; C/N ratio: 25–30; aeration rate: 0.15 Lmin\({}^{-1}\) kg\({}^{-1}\) TS & Evaluation of composing parameters of DG from 3 depths: T of composing pile, TOC, TN, TK, TP, pH, ECs, NO\({}_{3}\)–N, and NH\({}_{4}\)+N. & NH\({}_{4}\)+N, TOC, and C/N decreased with the composing process, while TP, TK, and NO\({}_{3}\)–N increased. GI and SGI showed that raw DGs were toxic to plants, but the GI and SGI increased during the composing process. & [105] \\ \hline DG fraction (agricultural waste and distillery village) & DG was mixed with equal parts of peat and compost for 80 days & Compounding parameters: dry matter, OM, pH, ECs, and T; daily measurements of gaseous emissions. & DG shows a very good structure and proper C/N ratio for composting. & [106] \\ \hline DG fraction (agricultural waste and distillery village) & DG was mixed with equal parts of peat and compost for 80 days & Compounding parameters: dry matter, OM, pH, ECs, and T; daily measurements of gaseous emissions. & DG shows a very good structure and proper C/N ratio for composting. & The optimal conditions (pH = 7.7, moisture = 50\%) obtained experimentally were used to develop a mathematical model \\ \hline DG & 70\%DM (\omega/w); C/N ratio: 28, 31, 33 and 36; juice pulp, cattle slurry) & ON = 88.07\%; T measured every 15 min; aeration for 2 min by opening the Dewar jars & Dewar tests) to establish the startup conditions to transfer the procedure to an industrial scale. & production of compliance with standards of stabilization, sterilization and compost quality. \\ \hline Freesh, air-dried, and oven-dried DG (municipal organic waste) & A part of solid DG was taken for air-drying (20–30 \({}^{\circ}\)C), a part was treated in open heaps for 6 weeks, and the third part was dried at 70 \({}^{\circ}\)C in a laboratory oven until the weight of DG remained constant. & Sieving of compost DG showed that HM concentration increases with decreasing mesh sizes. The element concentration is higher in compost batches, while the water-extractability of nutrients, HM, and C is significantly lower in compost over dried DGs. A significant correlation was found between the dissolution of Zn, Ni, Ca, and Mg, pH of eluate, and DOC release (R \(>\) 0.7, \(p\) < 0.05). & Siewing of compost DG showed that HM concentration increases with decreasing mesh sizes. The element concentration is higher in compost batches, while the water-extractability of nutrients, HM, and C is significantly lower in compost over dried DGs. A significant correlation was found between the dissolution of Zn, Ni, Ca, and Mg, pH of eluate, and DOC release (R \(>\) 0.7, \(p\) < 0.05). & Siewing of compost DG showed that HM concentration increases with decreasing mesh sizes. The element concentration is higher in compost batches, while the water-extractability of nutrients, HM, and C is significantly lower in compost quality. & [107] \\ \hline DG & 100\%DM (\omega/w); C/N ratio: 28, 31, 33 and 36; juice pulp, cattle slurry) & 100\%DM (\omega/w); C/N ratio: 28, 31, 33 and 36; dye pulp, cattle slurry) & 100\%DM (\omega/w); C/N ratio: 2  
Integrating compost into a farm's nutrient management plan should aim to maximize the use of nutrients supplied. Adequate application of compost help farmers achieve good crop performance and avoid wasting money, and also avoid environmental harm. Compost is best suited for soils requiring OM and/or P and potash. Soil condition and condition of equipment prior to compost application should be considered, as well as calculating the nutrients supplied by the compost and subtracting them from the crop's need.