Exploring the metabolic capabilities of purple phototrophic bacteria during piggery wastewater treatment

Abstract

Purple phototrophic bacteria (PPB) are receiving an increasing attention due to their extraordinary metabolic capabilities for nutrient and carbon recovery from wastewaters. Batch experiments were herein performed to assess the influence of the type of radiation (photosynthetic active radiation (PAR), near-infrared radiation (NIR) and PAR using an UV-VIS absorbing filter), temperature (13 °C and 30 °C), type of metabolism (photoheterotrophic and chemoheterotrophic), type of inoculum (mixed culture and pure strain Rhodopseudomonas palustris) and wastewater load (1:5 and 1:10 dilutions) during piggery wastewater (PWW) treatment by PPB. The use of UV-VIS filtered PAR supported both a high content of bacteriochlorophyll in PPB and the highest total organic carbon (TOC) and total nitrogen (TN) removal efficiency (RE) (74 % and 37 %, respectively), but at lower maximum removal rates. Interestingly, PPB exhibited similar TOC-REs and TN-REs (73 % and 37 %, respectively) at 13 °C than at 30 °C (71 % and 45 %, respectively), at similar removal rates. Mixed cultures of PPB achieved a higher nutrient assimilation rate than R. palustris, supporting a total assimilation of the volatile fatty acids present in 10 folds diluted PWW. In brief, mixed cultures of PPB were highly efficient during PWW treatment, regardless of the type of radiation and temperature under photoheterotrophic growth.