Extracellular polymeric substance production in high rate algal oxidation ponds

Abstract

Integrated algal pond systems (IAPSs) combine anaerobic and aerobic bioprocesses to affect sewage treatment. The present work describes the isolation and partial characterisation of soluble extracellular polymeric substances (EPSs) associated with microalgal bacterial flocs (MaB-flocs) generated in high rate algal oxidation ponds (HRAOPs) of an IAPS treating domestic sewage. Productivity and change in MaB-flocs concentration, measured as mixed liquor suspended solids (MLSS) between morning (MLSS) and evening (MLSS) were monitored and the substructure of the MaB-flocs matrix examined by biochemical analysis and Fourier transform infrared spectroscopy (FT-IR). Results show that MaB-flocs from HRAOPs are assemblages of microorganisms produced as discrete aggregates as a result of microbial EPS production. Formation and accumulation of the EPS was stimulated by light. Analysis by FT-IR revealed characteristic carbohydrate enrichment of these polymeric substances. In contrast, FT-IR spectra of EPSs from dark-incubated MaB-flocs confirmed that these polymers contained increased aliphatic and aromatic functionalities relative to carbohydrates. These differences, it was concluded, were due to dark-induced transition from phototrophic to heterotrophic metabolism. The results negate microalgal cell death as a contributor to elevated chemical oxygen demand of IAPS treated water.

A Brief Review of Anaerobic Digestion of Algae for Bioenergy

“…Mechanical aeration can, by contrast, be energy-intensive (0.4-1.1 kWh 1 kg −1 O 2 ) [59]. Facultative ponds are shallow human-made ponds where the organic component of the effluent is converted to microalgal and bacterial biomass in microalgal-bacterial flocs (MaB-flocs) with a continuous exchange of O 2 and CO 2 between microalgae and reduction of odours and pathogenic microorganisms [59][60][61][62]. Microalgae require nitrogen (N) and phosphorus (P) and are highly efficient at removing both elements from municipal wastewater that can have typical concentrations of 30-40 mg•L −1 N and 5-10 mg•L −1 P [63].…”

Advanced oxidation as tertiary treatment for recovery of effluent from an integrated algal pond system

“…The HRAOP B which has HRT of 4‐d decants to ASP B (0.5‐d HRT) from where settled MaB‐floc‐containing biomass is recovered. A detailed description of system configuration and process flow has been reported elsewhere (Jimoh & Cowan, 2017; Mambo et al, 2014a).…”

“…Microbial interactions during anaerobic fermentation, bacterial oxidation and photosynthetic oxygenation produces effluent that can be reclaimed and reused and which is of the standard in South Africa for either discharge or irrigation established by the Department of Water and Sanitation (Mambo et al, 2014a). In addition, mixed liquor suspended solids generated in the high rate algal oxidation ponds (HRAOP) in the form of microalgal‐bacterial flocs (MaB‐flocs) is a valuable resource and of biotechnological importance (Jimoh & Cowan, 2017; Jimoh et al, 2019). Once harvested, this biomass can be valorised into products such as biofuels, animal feeds and fertilisers (Coppens et al, 2016; Van Den Hende et al, 2014; Wieczorek et al, 2015).…”

“…Similarly, efforts to upgrade the AIWPS in the City of St. Helena, California in 2006 never materialised (West et al, 2006), while uptake of EPS and associated HRAOP technology by local government bodies and industries in New Zealand has also been slow (Sutherland & Ralph, 2020). Despite data to show that inclusion of an appropriate tertiary treatment process, e.g., a MPS, while substantially increasing footprint, ensured IAPS‐treated water was of a quality suitable for reclamation or discharge to river (Jimoh & Cowan, 2017; Mambo et al, 2014a), it seems that water quality issues and in particular elevated TSS and to a lesser extent COD contributed to the status quo. Thus, a perception that algae‐based sanitation technologies do not allow for sufficient removal of MaB‐floc biomass from the effluent to ensure that discharge standards are met for total nutrient and TSS (Craggs et al, 2012; Meiring & Oellermann, 1995; Sutherland & Ralph, 2020).…”

Discard Coal as Filter Bed Material in Horizontal Subsurface Flow Constructed Wetlands: a Preliminary Study

“…The remaining gravel-and discard coal-containing wetlands received nutrient rich water from an advanced facultative pond (AFP) attached to the Belmont Valley WWTW integrated algae pond system (IAPS). Details on the configuration and operation of this IAPS have been described elsewhere (Mambo et al, 2014;Jimoh & Cowan, 2017;Laubscher & Cowan, 2020;Titilawo et al, 2021). Tap and AFP water was from 20 L reservoirs fed continuously and positioned to gravity-feed each of the four HSF CWs at a rate of 43 L/day.…”