Pre-digestion to enhance volatile fatty acids (VFAs) concentration as a carbon source for denitrification in treatment of liquid swine manure

Advances in downstream processes and applications of biological carboxylic acids derived from organic wastes

Recovering carboxylic acids derived from organic wastes from fermentation broth is challenging. To provide a reference for future study and industrial application, this review summarized recent advances in recovery technologies of carboxylic acids including precipitation, extraction, adsorption, membrane-based processes, etc. Meanwhile, applications of recovered carboxylic acids are summarized as well to help choose suitable downstream processes according to purity requirement. Integrated processes are required to remove the impurities from the complicated fermentation broth, at the cost of loss and expense. Compared with chemical processes, biological synthesis is better options due to low requirements for the substrates. Generally, the use of toxic agents, consumption of acid/alkaline and membrane fouling hamper the sustainability and scale-up of the downstream processes. Future research on novel solvents and materials will facilitate the sustainable recovery and reduce the cost of the downstream processes.

Fe(III)/Fe(II) forwarding a new anammox-like process to remove high-concentration ammonium using nitrate as terminal electron acceptor

The study demonstrated a novel anammox-like process to remove high-concentration ammonium using nitrate as terminal electron acceptor under Fe(III)/Fe(II) cycle. Compared with NO₂^- in common anammox, NO₃^- used here is more available in practice, suitable for in-situ removal of high-concentration NH₄⁺ in a single anaerobic system. The NO_x^- and Fe(II) produced from Feammox [Fe(III) reduction coupled to anaerobic ammonium oxidation] subsequently react together via NO_x^--dependent Fe(II) oxidation to regenerate Fe(III) that potentially stimulates next round of Feammox. However, these processes couldn't be lasting due to inadequate Fe(III) regeneration because NO_x^- is non-dominant product during Feammox. In this study NO₃^- was added to supplement the insufficient NO_x^- to enhance Fe(III) regeneration and remove nitrogen successively. Results showed that periodically adding nitrate caused oscillations between Fe(III) and Fe(II) in the sludge, implying Fe(III) regeneration and consumption. Consequently, nitrogen removal of the digester with an initial total nitrogen of 1036.7 mg/L reached 90.1% after 98-day operation, much higher than that of control (41.6%) without NO₃^- addition. Adding NO₃^- in the digester to trigger Fe(III)/Fe(II) cycle for removing ammonium is just equivalent to an anammox-like process using NO₃^- as terminal electron acceptor to oxidize NH₄⁺.