Algal Remediation of Wastewater Produced from Hydrothermally Treated Septage

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

Quantitative Photoresponse of the First Photosynthetic Biomaterials: Physical Measurements and Analysis of Microalgae Systems

Herein, results of photoinduced pH oscillatory phenomena of microalgae in laboratory systems are presented. Microalgae are an extremely complex biomaterial in which light-induced quantum mechanical processes induce changes in the surrounding aqueous environment (medium). A phenomenological understanding of the photoresponse by a quantitative study of pH oscillations of the medium is provided. The biochemical processes of algal metabolism and photosynthesis and the impact of light on a nitrate-enriched medium are examined. pH variations in the external medium and the impact on future applications of microalgae are presented. External pH dominantly impacts conductivity in the solution of algal biophotovoltaic devices. This is the first dynamic study of the light-induced pH behavior of microalgae with direct relevance to carbon capture, biophotovoltaic electricity generation, and quantum photosynthesis

Challenges and Process Economics for Algal Carbon Capture with Novel Integration: Hydrothermal Carbonization

A techno-economic analysis (TEA) of the integration of hydrothermal carbonization of waste biomass with an algal bioreactor is presented. Analyses of qualitative data from a two-m3 tubular photobioreactor constructed at Honda R&D Americas in Raymond, Ohio, USA, indicated that microalgal nutrient cost was a key economic challenge. The use of hydrothermal carbonization (HTC) of solid biowastes to provide lower cost nutrients was modeled. The TEA used results of previous work culturing microalgae in HTC process water, along with other data from the Honda algal bioreactor. Assumption for the scope of the analysis included capture of all carbon emissions from the Honda Marysville Auto Plant in Marysville, Ohio and application of a small onsite power plant using HTC solids to provide electricity and additional CO2 for the bioreactor system. Results indicated that HTC integration could decrease total operating costs of the bioreactor system by 17% and carbon capture costs by 11%. Additionally, results indicated the HTC system could contribute nearly 50% of key cost inputs (C, P, N and electricity) and increase EROI from 8.05 to 13.5