The primary objective of this research was to improve our understanding of the water quality effects of thermochemical bioenergy production processes that can be applied to wet organic-laden wastes, such as animal manures, municipal wastewater, and food processing wastes. In particular, we analyzed the impacts of a novel integrated process combining algal wastewater treatment with hydrothermal liquefaction (HTL) on the fate of emerging bioactive contaminants (e.g., pharmaceuticals, estrogenic compounds, antibiotic-resistance genes, etc.) and the potential for wastewater reuse. We hypothesized and then confirmed that the elevated temperature and pressure of an HTL process can effectively convert the bioactive organic compounds into bioenergy products or otherwise break them down to inactive forms. High performance liquid chromatography (HPLC) with a photodiode array (PDA) detector was used to quantify emerging contaminants (florfenicol, ceftiofur, and estrone) before and after HTL treatment showed the removal of tested bioactive compounds to below detection limits when HTL was operated at 250°C for 60 min or at 300°C for ≥ 15 min. Complete breakdown or inactivation of antibiotic-resistance genes in wastewaters by the HTL process was also obtained at all tested HTL conditions (250-300°C, 15-60 min reaction time). The presence of HTL feedstocks such as swine manure or Spirulina algae reduced the removal of bioactive compounds and plasmid DNA when HTL was operated at 250°C for a short retention time (15 min). However, this effect was minimal when HTL was operated at 250°C for 60 min or at 300°C for ≥ 15 min. Detailed analysis of the aqueous product of HTL, also called HTL wastewater (HTL-WW), showed the occurrence of hundreds of nitrogenous organic compounds (NOCs). Reference materials for nine of the most significant NOC peaks were obtained and used to positively identify and quantify their concentrations. The chronic cytotoxicity effects of these NOCs were evaluated using a Chinese hamster ovary (CHO) cell assay, and found that the rank order for chronic cytotoxicity of these NOCs was 3-dimethylaminophenol > 2,2,6,6-tetramethyl-4-piperidinone > 2,6-dimethyl-3-pyridinol > 2-picoline > pyridine > 1-methyl-2-pyrrolidinone > σ-valerolactam > 2-pyrrolidinone > ε-caprolactam. However, none of the individual NOC compounds exhibited cytotoxicity at concentrations found in HTL-WW. In contrast, the complete mixture of organics extracted from HTL-WW showed significant cytotoxicity, with our results indicating that only 7.5% of HTL-WW would induce a 50% reduction in CHO cell density. Further testing showed three out of eight tested NOCs could cause 50% inhibition of algal growth at their detected concentration in HTL-WW. In addition, we found that treatment of HTL-WW with a batch-fed algal bioreactor could effectively remove more than 99% of NOCs after seven days of operation and 40% of the CHO chronic toxicity. We also found that over 90% of the CHO toxicity could be eliminated by filtering with granular activated carbon (GAC) after algal bioreactor treatment. These post-treatments of HTL-WW synergistically integrate with HTL bioenergy production because both the GAC and the algal biomass from the bioreactor can potentially be fed back into HTL to generate additional biocrude oil, which facilitates beneficial reuse of the nutrient content of HTL-WW. All in all, this novel treatment approach offers significant advantages for reducing the potential toxicity risks associated with byproducts of HTL bioenergy production and for improving wastewater effluent quality for subsequent water reuse applications.
|Name||TR series (Illinois Sustainable Technology Center)|
- Emerging contaminants
- Water reuse
- Wastewater treatment
- Waste to energy