Aqueous Co-product Research Articles

Removal of pollutants from aqueous product of Co-hydrothermal liquefaction: Adsorption and isotherm studies

Hydrothermal liquefaction (HTL) is an attractive technology for the conversion of wet waste into biofuel and co-HTL has been touted to increase the quality of products. However, the recovery of energy from wastewater byproduct called aqueous co-product (ACP) is limited due to the presence of toxic inhibitory substances. Adsorption has been countenanced to remove these toxic compounds but there has not been a distinct comprehensive adsorption isotherm study to explain the interaction between the adsorbate molecules and the adsorbent sites. This study investigated the sorption mechanism of oxidizable reducing pollutants measured as chemical oxygen demand (COD); heavy metals (boron and copper); and phenols from ACP samples obtained from co-HTL of brewery trub (BT), and primary sludge (PS) onto granular and powdered activated carbon (GAC and PAC). Conventional isotherm models such as Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich were used for data analysis. Results indicated that the adsorptive capacity (qe) of PAC was greater than GAC in COD adsorption (BT−1947 > 234; BTPS−617 > 245; PS−289 > 207), boron adsorption (BTPS−70 > 7; PS−53 > 49), copper adsorption (BT−5 > 1; BTPS−3 > 2; PS−1.3 > 1.1) and phenol adsorption (BT−1340 > 356; BTPS−1587 > 253; PS−460 > 245) in mg/g, μg/g, μg/g, and μg/g respectively. Comparing the adsorption of pollutants onto PAC and GAC, this study observed that PAC followed the Temkin, and Dubinin-Radushkevich models in the adsorption of the four pollutants while GAC followed the Freundlich and Langmuir models in the adsorption of phenol and copper, and Temkin, and Dubinin-Radushkevich in the adsorption of COD and boron. This study proved that combining feedstock in HTL (co-HTL) does not only change the quality of the ACP but also changes the dynamics of the adsorption isotherms. The Free Energy Change (ΔG0) result showed a spontaneous reaction in the adsorption of copper and phenol. This study presents an adsorption equilibrium information for the interpretation of adsorption isotherms for the overall improvement of adsorption mechanism pathways and the effective design of adsorption systems for the treatment of ACP.

Co-Hydrothermal Liquefaction of Sewage Sludge and Beverage Waste for High-Quality Bio-energy Production

The environment continues to experience pollution from a variety of industries including the beverage and wastewater treatment industries. These industries produce organic wastes; hence, they are costly to manage. As a result, they are largely incinerated or sent to landfills, respectively causing environmental pollution, and shrinking landfill space. To prevent these occurrences and better manage these wastes, thermochemical conversion processes have been touted as a possible solution. One such process is hydrothermal liquefaction (HTL). HTL is a process that converts wet waste biomass feedstocks at high temperature and pressure into biocrude oil, a solid residue (i.e., biochar), an aqueous co-product (i.e., wastewater, ACP), and vented gas. This study assessed the co-HTL of beverage waste with sewage sludge. Two beverage wastes: brewery trub (BT) and winery rose lees (RL) were co-liquefied with primary sludge (PS) and return activated sludge (RAS) at 300 °C, 90% water content, 30-min residence time, and co-HTL ratios (100/0, 75/25, 50/50, 25/75, and 0/100). The individual maximum yields of biocrude were PS (14.8%), BT (10.37%), RL (5.4%), and RAS (4.29%). In all cases, biocrude and biochar produced a higher heating value (HHV) greater than those of the original feedstocks. During the co-HTL experiments, a positive synergistic effect in terms of crude yield was observed between co-HTL of BT and PS; BT and RAS; and RL and PS while there was no appreciable effect in RL and RAS. Maximum yields of 15.45% and 15.14% were observed in the biocrude of co-liquefied BT and PS at 75/25 and 50/50 respectively. Co-HTL led to an increase in the HHV of the biocrude and biochar, and total organic carbon of ACP. The results of this study represent a favorable method for the simultaneous valorization of both sewage sludge and beverage waste into bioenergy products.

The individual and synergistic impacts of feedstock characteristics and reaction conditions on the aqueous co-product from hydrothermal liquefaction

We examined the individual and synergistic impacts of reaction conditions and microalgal feedstock characteristics, including previously unreported combinations of variables, on the yield and properties of aqueous co-product (ACP) from hydrothermal liquefaction. Explicitly, we measured the effects of temperature (150 to 350∘C), reaction time (1 to 100min), slurry concentration (30 and 120 g Lrxn−1), biochemical composition (5.2 to 28.5 wt.% lipid, 14.7 to 50.9 wt.% protein), and species identity (Nannochloropsis, Chlorella, and Spirulina) on ACP characteristics. Measured properties included gravimetric yield, elemental (CHNSOP) recoveries, NH4+-N and PO43−-P recoveries, and pH. The impacts of slurry concentration and species identity on the properties of ACP produced from microalgae are examined in-depth for novel combinations of reaction variables, with all probed variables affecting ACP yield and composition. Temperature exhibited the most influence, followed by time (at 200∘C) and biochemical composition (at 300∘C). Lower slurry concentration led to increased ACP yields and recovery of NH4+-N, total nitrogen, PO43−-P, total phosphorus, and sulfur; in fact, the data suggested that increased slurry concentration promotes Maillard reactions that inhibit NH4+-N recovery in the ACP and promote N recovery in the biocrude. High-lipid, 30 g Lrxn−1 slurries reacted at 200∘C for 31.6 min are a potential “win-win” set of conditions for both maximizing key ACP-recyclability metrics while limiting N and S recovery in the biocrude to <5 and <8%, respectively, and increasing the yield of high-quality biocrude. The results herein further illuminate ways in which reaction conditions and feedstock characteristics for HTL could be manipulated to engineer the ACP for desired nutrient content for direct recycling.

Hydrothermal Liquefaction and Photocatalytic Reforming of Pinewood (Pinus ponderosa)-Derived Acid Hydrolysis Residue for Hydrogen and Bio-oil Production

Pretreatment of lignocellulosic biomass (LCB) is a prerequisite for downstream bioconversion of its cellulosic components to second-generation biofuels. Acid hydrolysis pretreatment separates most of the hemicellulose and cellulose from lignin. However, the lignin-rich acid hydrolysis residue (AHR) may contain 20–50 wt % feedstock biomass. To improve the economics of LCB-based biorefinery, the AHR needs to be valorized. In this study, we have performed hydrothermal liquefaction (HTL) of AHR derived from the dilute acid treatment of pinewood for H₂ and bio-oil generation. A slurry of AHR at a biomass-to-water ratio of 1:30 was hydrothermally liquefied in the presence of a homogeneous Ni(NO₃)₂ catalyst at 250, 275, and 300 °C. About 16 wt % bio-oil and 51 mL of H₂ were generated at 300 °C and 60 min into the reaction. Based on elemental analysis, the higher heating value of bio-oil was found to be 29.8 MJ/kg. The aqueous coproduct generated during the HTL reaction was treated with activated carbon and subjected to the photocatalytic reforming (PR) process in the presence of a Pt/TiO₂ catalyst that produced an additional 90 mL of H₂ at NTP conditions. Preliminary calculations were performed to understand the energy recovery in terms of the products generated based on the total energy consumed for both HTL and PR processes.

Evaluating the Impacts of ACP Management on the Energy Performance of Hydrothermal Liquefaction via Nutrient Recovery

Hydrothermal liquefaction (HTL) is of interest in producing liquid fuels from organic waste, but the process also creates appreciable quantities of aqueous co-product (ACP) containing high concentrations of regulated wastewater pollutants (e.g., organic carbon, nitrogen (N), and phosphorus (P)). Previous literature has not emphasized characterization, management, or possible valorization of ACP wastewaters. This study aims to evaluate one possible approach to ACP management via recovery of valuable scarce materials. Equilibrium modeling was performed to estimate theoretical yields of struvite (MgNH4PO4·6H2O) from ACP samples arising from HTL processing of selected waste feedstocks. Experimental analyses were conducted to evaluate the accuracy of theoretical yield estimates. Adjusted yields were then incorporated into a life-cycle energy modeling framework to compute energy return on investment (EROI) for the struvite precipitation process as part of the overall HTL life-cycle. Observed struvite yields and residual P concentrations were consistent with theoretical modeling results; however, residual N concentrations were lower than model estimates because of the volatilization of ammonia gas. EROI calculations reveal that struvite recovery is a net-energy producing process, but that this benefit offers little to no improvement in EROI performance for the overall HTL life-cycle. In contrast, corresponding economic analysis suggests that struvite precipitation may be economically appealing.

Evaluation of Aqueous Product from Hydrothermal Liquefaction of Cardboard as Bacterial Growth Medium: Co-Liquefaction of Cardboard and Bacteria for Higher Bio-Oil Production

Hydrothermal liquefaction (HTL) processing of lignocellulosic biomass to bio-oil produces aqueous co-product (AP) which contains significant (~40 wt%) carbon from the original feedstock. This study evaluates macro and micronutrient composition of AP from Ca(NO3)2 catalyzed HTL of cardboard (CbAP) to cultivate bacteria. HPLC, GC-MS and ICP-MS analysis of CbAP revealed presence of C1-C3 carboxylic acids, aldehydes, ketones, phenolics, sub-optimal phosphorous and bio-incompatible levels of calcium. Dilutions (5 - 80 vol%) of detoxified CbAP (DTP-CbAP) in potassium phosphate buffer (pH 7.2) were supplemented with 50 mg·mL-1 of yeast extract and inoculated with metabolically versatile Enterobacter species. The cultures were incubated at 25°C under aerobic conditions. A maximum 9.4 fold increase in the dry cell weight was observed in DTP-CbAP-15 vol%. Co-liquefaction of the bacteria with cardboard in 1:1 and 1:3 weight ratios each produced ~33% more total bio-oil. These had higher HHVs of 34.11 and 31.05 MJ·kg-1, respectively compared with bio-oil from cardboard feedstock alone which had HHV of 30.61 MJ·kg-1. The study highlights the challenges in cultivating microbes in AP from HTL of lignocellulosic biomass (LCB) and the possibility to integrate microbial capture and recycle of the AP carbon for enhanced bio-oil production and quality.

Low temperature hydrothermal pretreatment of algae to reduce nitrogen heteroatoms and generate nutrient recycle streams

A two-stage hydrothermal liquefaction process was used to reduce nitrogen heteroatoms in algae biocrude and generate an aqueous co-product stream for algae cultivation. A low temperature liquefaction pretreatment (PT: 125–225°C, 0.5–30min) hydrolyzed proteins and partitioned nitrogen to the aqueous phase, which was separated and analyzed for nutrient and toxin concentrations. The retained solids (20%) were subjected to hydrothermal liquefaction (HTL) in the second step at 350°C for 60min. The low temperature pretreatment was most effective at higher temperatures and holding times (225°C, 15min), removing 45% of the nitrogen present in the algae solids, while retaining 59% of the solid mass, yet reduced overall bio-oil yields by 35 to 71% relative to single stage HTL. Experiments conducted in two-chamber reactors with increased heating rates, resulted in similar nitrogen removal levels at shorter residence times (250°C, 5min). When coupled with high-temperature HTL, pretreatment improved the elemental content of the biocrude by increasing the total nitrogen removed and reducing nitrogen heteroatom content by 26–28%, compared to HTL alone. The aqueous co-product stream was analyzed for nutrient availability and indicated potential for recycle and algae cultivation due to its high nitrogen and phosphorus levels, moderate pH, and low inhibitory compound concentrations.

Hydrothermal Treatment for Production of Aqueous Co-Product and Efficient Oil Extraction from Microalgae

Hydrothermal Treatment for Production of Aqueous Co-Product and Efficient Oil Extraction from Microalgae

Microbial utilization of aqueous co-products from hydrothermal liquefaction of microalgae Nannochloropsis oculata

Hydrothermal liquefaction of algae biomass is a promising technology for the production of sustainable biofuels, but the non-oil, aqueous co-product of the process has only been examined to a limited extent. The aqueous phase from liquefaction of the alga Nannochloropsis oculata (AqAl) was used to make growth media for model heterotrophic microorganisms Escherichia coli, Pseudomonas putida, and Saccharomyces cerevisiae. Growth rates, yields, and carbon/nitrogen/phosphorus uptake were measured. E. coli and P. putida could grow using AqAl as the sole C, N, and P source in media containing 10vol.%–40vol.% AqAl with the best growth occurring at 20vol.%. S. cerevisiae could grow under these conditions only if the media were supplemented with glucose. The results indicate that in a biorefinery utilizing algae liquefaction, the aqueous co-product may be recycled via microbial cultures with significantly less dilution than previously published methods.

Evaluation of microalgae cultivation using recovered aqueous co-product from thermochemical liquefaction of algal biomass

This study characterized the ACP stream from the TCL of Spirulina and evaluated its potential as a nutrient source for cultivation of microalgae. TCL of 100 g of dry Spirulina resulted in 40% BioOil and 429.80% ACP. The ACP was found to have high nitrogen (16,200 mg L(-1)), phosphorus (795 mg L(-1)), potassium (11,260 mg L(-1)) and secondary and micronutrients. Growth media were prepared using ACP as sole nutrient source in deionized water at 0.2%, 0.33%, 1%, and 10% v/v concentration and compared with a standard growth medium (BG 11) for algal cultivation. Chlorella minutissima was grown in these media for 12 days and monitored for biomass concentration, total chlorophyll and lipids. Biomass productivities with the ACP added media at 0.2% and 0.1% concentration were 0.035 and 0.027 g L(-1) d(-1), respectively, compared to 0.07 g L(-1) d(-1) in BG 11.