Biofuels production 191
Remedy a) Reduce feeding rate. b) Stabilize temperature. c) Remove scum. Have patience. Never put acid into the digester. a) Dilution or low loading makes ammonia toxicity less critical. b) Stirring, dilution or low loading reduces viscosity. c) As discussed earlier in Problems 8 and 9. d) Raise the temperature by heating. e) Do not change the slurry mixture of a working digester.Cause a) Adding raw material too fast. b) Wide temperature fluctuation. c) Build-up of scum. Initial raw material too alkaline. a) Increase in toxicity with retention time. b) Increase in solid content. c) pH too acidic or too alkaline. d) Low temperature. e) Addition of significant quantity of different types of feed material to a working digester, for example, addition of an equal mass of vegetable matter to the digester utilizing pig waste.Table 4.19 Problems with the operation of the biogas plant (adapted from Tata Energy Research Institute 1982) (continued) Problem 8. pH too acidic (pH < 6) 9. pH too alkaline (pH > 7) 10. Slow rate of gas production or no gas production.