Abstract
Hydrothermal carbonization (HTC) is a promising technology to convert wet wastes like septic tank wastes, or septage, to valuable platform chemical, fuels, and materials. However, the byproduct of HTC, process liquid, often contains large amount of nitrogen species (up to 2 g/L of nitrogen), phosphorus, and a variety of organic carbon containing compounds. Therefore, the HTC process liquid is not often treated at wastewater treatment plant. In this study, HTC process liquid was treated with algae as an alternative to commercial wastewater treatment. The HTC process liquid was first diluted and then used to grow Chlorella sp. over a short period of time (15 days). It was found that the algae biomass concentration increased by 644 mg/L over the course of 10 days, and which subsequently removed a majority of the nutrients in the HTC process liquid. Around 600 mg/L of algal biomass was collected in the process liquid at the end of treatment (day 15). Meanwhile, chemical oxygen demand (COD), total phosphorous, total Kheldjal nitrogen, and ammonia were reduced by 70.0, 77.7, 82.2, and 99.0% by fifteen days compared to the untreated wastewater, respectively. This study demonstrates that HTC process liquid can be treated by growing algae creating a potential replacement for expensive synthetic nutrient feeds for algal production.
Highlights
Hydrothermal carbonization (HTC) is a wet treatment process conducted at 160–260 ◦C and at autogenous pressures
Note that the initial HTC liquid samples were diluted to avoid limiting the growth of the algae due to the high levels of salts found in the original sample [4]
This study has demonstrated that algal remediation of hydrothermal process water is effective at reducing the nutrient content of the HTC process liquid
Summary
Hydrothermal carbonization (HTC) is a wet treatment process conducted at 160–260 ◦C and at autogenous pressures. HTC is an attractive choice for these wet wastes as it does not require cost intensive drying prior to the treatment unlike pyrolysis, gasification, and combustion. Our recent research on HTC of septic tank wastes known as septage, as well as other’s studies on sewage wastes and manures, have shown concentration of phosphorus in hydrochar (carbon rich solids that are produced during HTC of biomass) solids and control of the nitrogen distribution (as protein fragments, nitrates, and ammonia), which are favorable for hydrochar as solid fertilizer [4,5,6]. Previous research has investigated using anaerobic digestion (AD) or wet air oxidation (WAO) of wastes to remediate the nutrients (or, pollutants) from the wastewater [7,8]. This work was undertaken to investigate alternative options for hydrothermal process liquid remediation
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