Process for the anaerobic fermentation of biogenic waste materials and plant for carrying out this process

1. A process for the anaerobic fermentation of biogenic waste materials, comprising:

a) mixing a liquid with a fermentation material containing the waste materials to obtain a fermentation material suspension, and anaerobically fermenting the fermentation material suspension in a fermenter to produce a digest;

b) dewatering the digest by means of a dewatering device to obtain a press water and a press cake having a dry matter proportion increased with respect to the digest; and

c) subjecting the press water to a solids separation to obtain a residual liquid having a dry matter proportion reduced with respect to the press water, the dry matter proportion of the residual liquid being at most 15% by weight,

wherein the residual liquid is used at least in part for the mixing according to step a).

2. The process as claimed in claim 1 , performed continuously or semi-continuously.

3. The process as claimed in claim 1 , wherein the solids separation according to step c) is performed by means of filtration and/or by means of screening, and the residual liquid is formed by the filtrate of the filtration or by the screen underflow of the screening.

4. The process as claimed in claim 1 , wherein the press water obtained in step b) and/or the residual liquid obtained in step c) is temporarily stored before the respective following step.

5. The process as claimed in claim 1 , wherein step a) comprises mixing the fermentation material in a mixing device with the residual liquid and optionally further water to obtain the fermentation material suspension.

6. The process as claimed in claim 1 , wherein the dry matter proportion in the fermentation material suspension in step a) is between 25 and 35% by weight.

7. The process as claimed in claim 1 , wherein a part of the digest, the press cake obtained during the dewatering according to step b), the residual solids obtained in the solids separation in step c), or a mixture thereof is added to the fermentation material or the fermentation material suspension as inoculum material.

8. The process as claimed in claim 1 , further comprising determining and setting to a desired value one or more parameters of the residual liquid, said parameters being selected from the group consisting of:

pH,

buffer capacity,

H 2 S content,

ammonium ion content or ammonia content,

content of fatty acids, and

content of short-chain carboxylic acids.

9. The process as claimed in claim 1 , further comprising adding at least one of the following auxiliaries or additives to the residual liquid:

acid,

lye,

buffer,

micronutrient elements or trace elements, and

macronutrient elements.

10. The process as claimed in claim 3 , wherein the solids separation according to step c) is performed by means of screening having two or more screening stages, wherein, in a first screening stage c1), a coarse fraction of solids components is separated off from the press water and from the suspension remaining from the stage c1) as screen underflow, in a subsequent second screening stage c2), a fine fraction is separated off in order to obtain the residual liquid.

11. The process as claimed in claim 1 , wherein the solids separation according to step c) is performed using a vibrating screen and/or a shaking screen.

12. The process as claimed in claim 10 , wherein the solids separation according to step c) is performed using a vibrating screen and/or a shaking screen.