Impact of hydraulic retention time on community assembly and function of photogranules for wastewater treatment
Trebuch, L.M. ; Oyserman, B.O. ; Janssen, M. ; Wijffels, R.H. ; Vet, L.E.M. ; Fernandes, T.V. - \ 2020
Water Research 173 (2020). - ISSN 0043-1354
Extracellular polymeric substances - Functional network - Metagenomics - Microalgae and cyanobacteria - Microbial ecology - Phototrophic granulation
Photogranules are dense, spherical agglomerates of cyanobacteria, microalgae and non-phototrophic microorganisms that have considerable advantages in terms of harvesting and nutrient removal rates for light driven wastewater treatment processes. This ecosystem is poorly understood in terms of the microbial community structure and the response of the community to changing abiotic conditions. To get a better understanding, we investigated the effect of hydraulic retention time (HRT) on photogranule formation and community assembly over a period of 148 days. Three laboratory bioreactors were inoculated with field samples from various locations in the Netherlands and operated in sequencing batch mode. The bioreactors were operated at four different HRTs (2.00, 1.00, 0.67, 0.33 days), while retaining the same solid retention time of 7 days. A microbial community with excellent settling characteristics (95–99% separation efficiency) was established within 2–5 weeks. The observed nutrient uptake rates ranged from 24 to 90 mgN L−1 day−1 and from 3.1 to 5.4 mgP L−1 day−1 depending on the applied HRT. The transition from single-cell suspension culture to floccular agglomeration to granular sludge was monitored by microscopy and 16S/18S sequencing. In particular, two important variables for driving aggregation and granulation, and for the structural integrity of photogranules were identified: 1. Extracellular polymeric substances (EPS) with high protein to polysaccharide ratio and 2. specific microorganisms. The key players were found to be the cyanobacteria Limnothrix and Cephalothrix, the colony forming photosynthetic eukaryotes within Chlamydomonadaceae, and the biofilm producing bacteria Zoogloea and Thauera. Knowing the makeup of the microbial community and the operational conditions influencing granulation and bioreactor function is crucial for successful operation of photogranular systems.
Regeneration and reuse of microbial extracellular polymers immobilised on a bed column for heavy metal recovery
Ajao, Victor ; Nam, Kang ; Chatzopoulos, Paraschos ; Spruijt, Evan ; Bruning, Harry ; Rijnaarts, Huub ; Temmink, Hardy - \ 2020
Water Research 171 (2020). - ISSN 0043-1354
Biosorption - Column - Extracellular polymeric substances - Ion exchange mechanism - Metal adsorption
Microbial extracellular polymeric substances (EPS) have gained increasing attention for various water treatment applications. In this study, EPS produced from nitrogen-limited glycerol/ethanol-rich wastewater were used to recover Cu2+ and Pb2+ from aqueous solutions. Continuous flow-through tests were conducted on a column packed with silica gel coated with polyethyleneimine, to which EPS were irreversibly attached as shown by optical reflectometry. These immobilised EPS excellently adsorbed Cu2+ and Pb2+, with 99.9% of influent metal adsorbed before the breakthrough points. Metal desorption was achieved with 0.1M HCl, with an average recovery of 86% for Cu2+ and 90% recovery for Pb2+. For the first time, we successfully showed the possibility to regenerate and reuse the immobilised EPS for five adsorption-desorption cycles (using Cu2+ as an example) with no reduction in the adsorbed amount at the breakthrough point (qbp). Based on the mass balance of the associated metal ions participating in the adsorption process, ion exchange was identified as the major mechanism responsible for Cu2+ and Pb2+ adsorption by EPS. The results demonstrate the potential of wastewater-produced EPS as an attractive and perhaps, cost-effective biosorbent for heavy metal removal (to trace effluent concentrations) and recovery (86–99%).
Natural flocculants from fresh and saline wastewater : Comparative properties and flocculation performances
Ajao, Victor ; Bruning, Harry ; Rijnaarts, Huub ; Temmink, Hardy - \ 2018
Chemical Engineering Journal 349 (2018). - ISSN 1385-8947 - p. 622 - 632.
Bioflocculant - Extracellular polymeric substances - Industrial wastewater - Mixed culture - Natural polyelectrolyte - Resource recovery
Natural flocculants, due to their eco-friendliness, have gained increasing attention for (waste) water treatment and are promising alternatives to oil-based synthetic flocculants. We systematically investigated simultaneous industrial wastewater treatment with the production of microbial extracellular polymeric substances (EPS) as natural flocculants. EPS were produced in two membrane bioreactors, respectively treating fresh and saline synthetic wastewater from biodiesel and (bio)ethanol industries. From each reactor, soluble and bound EPS fractions were extracted, purified and characterised for their functionalities, molecular weights and charge densities using Fourier transform infrared (FTIR), size exclusion chromatography and colloid titration, respectively. High removal of chemical oxygen demand (COD) was achieved in both reactors (93–95%), with 5.8–7.6% of the inlet COD recovered as EPS. FTIR spectroscopy reveals these EPS as a mixture of proteins and polysaccharides, possessing carboxyl, hydroxyl and amine groups. These functional groups, which provided a net anionic charge density (1.5–2.9 meq/g at neutral pH), coupled with EPS mixed molecular weight (MW) distribution: high (>1000 kDa), medium (1000–100 kDa) and low (<100 kDa) MW fractions, make them promising flocculants. Extracted EPS showed good flocculation of non-saline kaolin suspension (74–89% turbidity reduction) and excellent flocculation of saline kaolin suspension (88–97%), performances comparable to anionic polyacrylamide. The results show the possibility for wastewater treatment plants to combine wastewater treatment with the production of valuable flocculants.
Oil spill dispersants induce formation of marine snow by phytoplankton-associated bacteria
Eenennaam, J.S. van; Wei, Yuzhu ; Grolle, K.C.F. ; Foekema, E.M. ; Murk, A.J. - \ 2016
Marine Pollution Bulletin 104 (2016)1-2. - ISSN 0025-326X - p. 294 - 302.
Deepwater horizon - Dispersants - Extracellular polymeric substances - Marine phytoplankton - Marine snow - Symbiotic bacteria
Unusually large amounts of marine snow, including Extracellular Polymeric Substances (EPS), were formed during the 2010 Deepwater Horizon oil spill. The marine snow settled with oil and clay minerals as an oily sludge layer on the deep sea floor. This study tested the hypothesis that the unprecedented amount of chemical dispersants applied during high phytoplankton densities in the Gulf of Mexico induced high EPS formation. Two marine phytoplankton species (Dunaliella tertiolecta and Phaeodactylum tricornutum) produced EPS within days when exposed to the dispersant Corexit 9500. Phytoplankton-associated bacteria were shown to be responsible for the formation. The EPS consisted of proteins and to lesser extent polysaccharides. This study reveals an unexpected consequence of the presence of phytoplankton. This emphasizes the need to test the action of dispersants under realistic field conditions, which may seriously alter the fate of oil in the environment via increased marine snow formation.