Table 3 Results of the survey of operators of biogenic waste-treating biogas plants regarding foam formation in digesters
From: Foam formation in full-scale biogas plants processing biogenic waste
| Description of surveyed biogas plants | Survey results | |||||||
|---|---|---|---|---|---|---|---|---|
| Biogas plant | Substrates | Capacity | Foam formation | Frequency of foam formation | Suspected causes of foaming | Foam control measures | Application of anti-foaming agents | |
| Saxony | ||||||||
| 1 | Sewage sludge, separately collected biowaste and commercial waste | 55,000 t/a | Two digesters á 2,300 m3 | Yes | Once a year | Surfactants, animal protein, etc. | Dilution, lowering the level in digester, addition of lime | Yes |
| 2 | See information to BP E in Table 1 | Yes | Always | Unknown | Agitation | No | ||
| 3 | Cattle manure, poultry manure, grease separator contents | 28,000 t/a | Two-stage, mesophilic | Yes | Only at the beginning | Unknown | NA | NA |
| 4 | See information to BP D in Table 1 | Yes | Formerly | Nutrient deficiency, overloading | ‘Starvation diet’, adjustment of the feeding system | No | ||
| 5 | Poultry manure, green waste, kitchen waste, grease separator contents, old food, paper sludge | 40,000 t/a | Two-stage, mesophilic | NA | ||||
| 6 | NA | NA | ||||||
| Saxony-Anhalt | ||||||||
| 7 | Biowaste, food waste from discounter | 50,000 t/a | Coupled dry and liquid production | Yes | Once | No more information available | ||
| 8 | Biogenic waste | 30,000 t/a | Single-stage, thermophilic | No | ||||
| 9 | Remains of the bioethanol production | 100,000 t/a | NA | No (foaming problems only in the desulfurization step) | ||||
| 10 | Mash from a distillery, process wastewater from a potato peeling plant | 2,400 m3/a | Single-stage (1,200 m3) | Yes | NA | Tensides | NA | NA |
| 11 | Poultry waste (litter from the poultry keeping, flotation tailings, and wastewater from the slaughter), grease and pizza residues | 12.400 t/a | Two-stage, mesophilic | Yes | Twice per year | Nutrient deficiency | Addition of a nutrient mixture | Yes |
| 12 | Green waste, commercial waste, biowaste | 21.000 t/a | Single-stage, mesophilic | Yes | Regularly | Unknown | Dilution of substrate with water | Yes |
| 13 | Food, commercial waste | 46.000 t/a | NA | Yes | Once | Overfeeding | Reduction of the substrate loading | No |
| Thuringia | ||||||||
| 14 | Leftovers | 72.000 t/a | Single-stage, mesophilic | Yes | Sometimes | NA | NA | NA |
| 15 | NA | NA | NA | NA | ||||
| 16 | Swine manure, paper fiber residual materials, slaughterhouse waste | NA | Single-stage, mesophilic | Yes | Formerly | Protein-containing slaughterhouse waste, cellulosic wastes from a paper mill | The operator tried miscellaneous, but nothing helped considerably | NA |
| 17 | Process wastewater from paper processing | NA | NA | No (foaming problems only in the desulfurization step) | ||||
| 18 | Cattle manure, biowaste, grease separator contents | 30.000 t/a | Single stage (2× 800 m3), thermophilic | Yes | Regularly | Grease separator contents | Reduction of the substrate loading | NA |