Advanced anaerobic digestion to carboxylic acids

A method comprising:

• converting, utilizing a microorganism, a substrate into a carboxylic acid contained in a fermentation stream comprising the carboxylic acid, water, and solids;
• removing the solids from the fermentation stream to form a substantially solids-free permeate comprising the carboxylic acid and water;
• treating the permeate with a first stream comprising a phosphine oxide by directing the permeate to a first side of a membrane having a thickness defined by a first side and a second side, and directing the first stream to the second side of the membrane;
• and
• maintaining a pH of the permeate between greater than 2.5 and less than 5 without the addition of an acid or a base;
• wherein:
• a concentration of the solids in the fermentation stream is between greater than 12 wt % and less than or equal to 30 wt %,
• the removing is performed using a rotating ceramic disk filter,
• the treating is performed using a volumetric ratio of the permeate to the first stream between 1:100 and 1:10,
• the carboxylic acid is present as a water-soluble species in the permeate,
• the treating results in the transferring of the carboxylic acid from the permeate, through the membrane thickness, to the first stream,
• the transferring results in the maintaining of the pH range,
• the treating results in the forming of a water stream and a second stream comprising the phosphine oxide and the carboxylic acid, and
• the membrane is not a hollow fiber membrane.