Cyanobacterial biocomposites for in situ treatment of domestic wastewater

Abstract

Centralised water treatment infrastructure is increasingly being put under strain due to population growth. In situ treatment (i.e. a distributed treatment network) may minimise or even negate the need for centralised infrastructure. Cyanobacteria grown in open-ponds and photobioreactors are used for wastewater treatment; however these cultivation systems struggle with batch consistency and have a high capital cost. Biocomposites (biomass immobilised on a solid substrate within a semi-porous matrix) theoretically support increased active biomass within a more compact space and prevent cell wash-out, thereby increasing bioremediation efficiency. Wild-type Synechococcus elongatus (strains PCC 7942 and CCAP 1479/1A) and a novel engineered strain (SBG363; designed to overproduce and excrete sucrose) were trialled as potential bioremediation biocomposites. Commercial latex-based binders (AURO 320 and 321) were used for biocoatings formulation, and applied to a selection of natural and synthetic textiles to form textile-based biocomposites. Biomass growth was increased by up to 800%, retaining up to 97% of biomass after 72 hours. Sucrose output from S. elongatus SGB363 was unaffected. Wild-type immobilised biomass supported up to 80% greater CO2 sequestration over a 20-day period than its suspension culture control. However, after three and six days of immobilisation there were no significant differences in total protein content, CO2 removal, or orthophosphate uptake per cell between immobilised and suspension treatments. Whole transcriptome sequencing (RNA-Seq) was attempted to determine the genetic response of S. elongatus surviving within a biocoating. However, immobilised samples had very low RNA integrity number equivalents that prevented differential gene expression analysis. This research shows that cyanobacteria textile biocomposites are a promising solution for process intensification in the wastewater treatment industry, and addresses concerns regarding environmental safeguarding. Metabolically active biocomposites can be used for de-centralised wastewater treatment applications thereby alleviating problems associated with Victorian era infrastructure without creating an additional environmental burden.