Optimization of wastewater feeding for single-cell protein production in an anaerobic wastewater treatment process utilizing purple non-sulfur bacteria in mixed culture condition

This study's objective is to analyze what times of feeding and withdrawal of residual waters on the treatment tank are optimal for their treatment by means of purple non-sulfur bacteria.

Wastewater treatment plant

This is a photosynthetic tank treatment, which is a kind of high-yield oxidation tank treatment. This treatment was selected due to the use by purple non-sulfur bacteria of VFAs (volatile fatty acids) as substrate, which reduces the generation of odorous gases and greenhouse effect gases that tend to be found specially on the 1st tank in the conventional chain.

This process also presents other advantages, such as the use of the cellular mass of purple non-sulfur bacteria as manure, fish feeding or agricultural substrate.

The purple non-sulfur bacteria can grow together with acidogenic bacteria in microaerobic or anaerobic conditions. And if they are maintained as the dominant this is preferable on constant illumination conditions, as it eliminates the need for a pretreatment (reducing the generation of greenhouse and odorous gases).

The acidogenic bacteria are necessary because they generate the first reactive needed by the purple non-sulfur bacteria. Allowing their quimiotrophic growth by acidogenesis on the dark phase if the illumination isn't constant. Though this generates methane synthesis.

Rps. Palustris

The feeding and withdrawal of fecal waters in the tank can be an important factor in the state of bacterial communities and the process' yield. As it regulates the flux of nutrients in the media.

The bacteria used for this experiment was Rhodopseudomonas palustris. As it doesn't use glucose for carbon source, facilitating the identification of the changes in the media generated by the other microorganisms.

To check under which conditions a higher yield is obtained 3 different pathways were followed: Feeding at the beginning of the luminous phase and withdrawing at the end of the dark phase. Feeding at the beginning of the dark phase and withdrawing at the end of the luminous one. And feeding at the beginning of the luminous phase but withdrawing at the end of it.

A glucose medium was used as simulated wastewater along with a vitamin solution and the metallic probe.

The tests realized for measuring the yield were DOC and TOC (dissolved organic carbon and total organic carbon) which are a good indication of the reactions made by the different bacteria.

Laboratory conditions

A microalgal growth was observed to be a factor in the diminution of purple non-sulfur bacteria, which makes it's inhibition necessary for the stable use of said bacteria. For that the use of infrared rays or filters for the reduction of ultraviolet-visible radiation are suggested.

It's not essential to realize an acidogenic pretreatment independently, due to Rps. palustris' capacity to grow on a metabolite mixed culture environment through the use of acidogenic bacteria. The production of monocellular proteins was as it's higher when the residual waters were fed at the begining of the luminous phase, without any difference on when they are withdrawn. Wich makes this feeding the optimal.

Authors: Cristian M. Segura Rodríguez, Marta Juan Ordás, Javier Palomares Laguna, Jose Antonio Torres Llopis y Alejandro Quiles Campoy

Bibliografía:

Ryo Hondaa, Kensuke Fukushi, Kazuo Yamamoto

Optimization of wastewater feeding for single-cell protein production in an anaerobic wastewater treatment process utilizing purple non-sulfur bacteria in mixed culture condition

Integrated Research System for Sustainability Science (IR3S), The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan

Environmental Science Center, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan