Anaerobic digestion of post-hydrothermal liquefaction wastewater for improved energy efficiency of hydrothermal bioenergy processes.

Hydrothermal liquefaction (HTL) is a promising process for converting wet biomass and organic wastes into bio-crude oil. It also produces an aqueous product referred to as post-hydrothermal liquefaction wastewater (PHWW) containing up to 40% of the original feedstock carbon, which reduces the overall energy efficiency of the HTL process. This study investigated the feasibility of using anaerobic digestion (AD) to treat PHWW, with the aid of activated carbon. Results showed that successful AD occurred at relatively low concentrations of PHWW (≤ 6.7%), producing a biogas yield of 0.5 ml/mg CODremoved, and ∼53% energy recovery efficiency. Higher concentrations of PHWW (≥13.3%) had an inhibitory effect on the AD process, as indicated by delayed, slower, or no biogas production. Activated carbon was shown to effectively mitigate this inhibitory effect by enhancing biogas production and allowing digestion to proceed at higher PHWW concentrations (up to 33.3%), likely due to sequestering toxic organic compounds. The addition of activated carbon also increased the net energy recovery efficiency of AD with a relatively high concentration of PHWW (33.3%), taking into account the energy for producing activated carbon. These results suggest that AD is a feasible approach to treat PHWW, and to improve the energy efficiency of the HTL processes.

Chemical and biological characterization of wastewater generated from hydrothermal liquefaction of Spirulina.

Hydrothermal liquefaction (HTL) is an attractive method for converting wet biomass into petroleum-like biocrude oil that can be refined to make petroleum products. This approach is advantageous for conversion of low-lipid algae, which are promising feedstocks for sustainable large-scale biofuel production. As with natural petroleum formation, the water in contact with the produced oil contains toxic compounds. The objectives of this research were to: (1) identify nitrogenous organic compounds (NOCs) in wastewater from HTL conversion of Spirulina; (2) characterize mammalian cell cytotoxicity of specific NOCs, NOC mixture, and the complete HTL wastewater (HTL-WW) matrix; and (3) investigate mitigation measures to reduce toxicity in HTL-WW. Liquid-liquid extraction and nitrogen-phosphorus detection was used in conjunction with gas chromatography-mass spectrometry (GC-MS), which detected hundreds of NOCs in HTL-WW. Reference materials for nine of the most prevalent NOCs were used to identify and quantify their concentrations in HTL-WW. Mammalian cell cytotoxicity of the nine NOCs was quantified using a Chinese hamster ovary (CHO) cell assay, and the descending rank order for cytotoxicity was 3-dimethylamino-phenol > 2,2,6,6-tetramethyl-4-piperidone > 2,6-dimethyl-3-pyridinol > 2-picoline > pyridine > 1-methyl-2-pyrrolidinone > σ-valerolactam > 2-pyrrolidinone > ε-caprolactam. The organic mixture extracted from HTL-WW expressed potent CHO cell cytotoxic activity, with a LC(50) at 7.5% of HTL-WW. Although the toxicity of HTL-WW was substantial, 30% of the toxicity was removed biologically by recycling HTL-WW back into algal cultivation. The remaining toxicity of HTL-WW was mostly eliminated by subsequent treatment with granular activated carbon.

Improving bioenergy recovery from municipal wastewater with a novel cloth-filter anaerobic membrane bioreactor.

Anaerobic membrane bioreactors (AnMBR) have been used for treating high-strength industrial wastewater at full-scale and the potential to use them for mainstream municipal wastewater treatment presents an important opportunity to turn energy-intensive plants into net-energy producers. However, several limitations of the AnMBR technology have prevented their adoption in the municipal wastewater industry, namely, high membrane cleaning energy demand and low membrane flux. This study demonstrated a novel AnMBR configuration that uses a commercially available cloth filter technology to address the key limitations of cleaning energy and membrane flux. The cloth filter anaerobic membrane bioreactor (CFAnMBR) is comprised of an anaerobic fixed-film bioreactor coupled with a cloth filter membrane with nominal pore size of 5 µm. The pilot CFAnMBR was operated for 150 days through the winter at a municipal wastewater plant in central Illinois (minimum/average influent temperature 5/13°C). The CFAnMBR increased membrane flux by more than 2 orders of magnitude (3,649 ± 1,246 L per meter squared per hour) and reduced cleaning energy demand by 78%-92% (0.0085 kWh/m3) relative to previously reported AnMBR configurations. With the CFAnMBR, average chemical oxygen demand and total suspended solids removal were 66% and 91%, respectively, and were shown to be increased up to 88% and 96% by in-line coagulant dosing with ferric chloride. Average headspace methane yield was 154 mL CH4/g CODremoved by the end of the study period with influent temperatures of 11°C± 4°C. The CFAnMBR resolves major limitations of AnMBR technology by employing a commercially-available technology already used for other municipal wastewater treatment applications.

Utilizing bioaugmentation to improve performance of a two-phase AnMBR treating sewage sludge.

Bioaugmentation in the acid-phase of a two-phase anaerobic membrane bioreactor (AnMBR) treating primary sludge was investigated as a means for targeting and improving hydrolysis and acetogenesis. Bioaugmentation was carried out using a proprietary bioculture blend containing a mixture of hydrolytic, acidogenic, and acetogenic microorganisms. This mixture was added on its own and in combination with recycled anaerobic sludge from the methane-phase of the AnMBR. Both bioaugmentation strategies had a positive effect on overall hydrolysis (25-38%), and acid-phase acetic acid generation (31-52%) compared to operation without bioaugmentation. This led to subsequent increases in average methane production (10-13%), and greater average solids reduction (25-55%). Microbial community analysis using 16S Illumina MiSeq generated sequences revealed increased relative abundance of Acetobacter and Syntrophomonas species in bioaugmented communities, suggesting these to be key players in improvements in process performance. However, in general the relative abundance of bioaugmented microorganisms within bioaugmented communities was relatively low, highlighting the need to optimize the bioculture composition and dosage. Overall, bioaugmentation was found to benefit the conversion of primary sludge to methane, when initial solubility was relatively low. Future work should optimize the bioculture composition and dosing strategy to improve its effectiveness and long-term stability, and minimize associated operating costs.

Fate and transport of estrogenic compounds in an integrated swine manure treatment systems combining algal-bacterial bioreactor and hydrothermal processes for improved water quality.

An integrated manure treatment system, including a mixed algal-bacterial bioreactor (MABB) and hydrothermal processing of biomass solids, was found to remove 76.4-97.0% of the total estrogenic hormones (estrone (E1), 17ß-estradiol (E2), and estriol (E3)) from the liquid portion of animal manure (LPAM). The mixed biomass was converted into either biocrude oil with a yield up to 40% via hydrothermal liquefaction (HTL) or syngas with a yield up to 54% yield via catalytic hydrothermal gasification (CHG). Adding granular activated carbon (GAC) in the MABB enhanced the removal of estrogenic hormones (+ 7.2%), cytotoxicity (+ 58%), and heavy metals (+ 10.5%). After the integrated system with the MABB, HTL, and CHG processes, the overall percent removal of heavy metals from the LPAM ranged from 27.1 to 40.3%. The concentrations of potentially toxic heavy metals (lead (Pb), copper (Cu), zinc (Zn), cadmium (Cd), nickel (Ni), chromium (Cr)) in the aqueous phase after HTL and CHG tests ranged from 0.01 to 25.3 mg/L.

An overall isotherm for activated carbon adsorption of dissolved natural organic matter in water.

Design and analysis of activated carbon processes in water treatment often requires the adsorption isotherm for dissolved natural organic matter (NOM). Of the isotherm models available, the Summers and Roberts (SR) equation, capable of describing the adsorbent dose effect with the fewest parameters, has been successfully used to normalize NOM isotherm data. In this study, we show that the adsorbent dose in the SR equation can be eliminated as an intermediate variable and the initial concentration effect on NOM adsorption is then described explicitly. Comparing with the original SR equation, the derived isotherm equation is in a form more amenable to analysis. To ensure that the prediction is physically attainable, we introduced the limiting adsorption capacity by taking the adsorbent pore volume and size exclusion into consideration. Subsequently, we develop a simple relationship that can be used to determine the minimum adsorbent usage required for any desirable level of treatment. By comparing with extensive isotherm data previously published by Li et al. [2003a. Polydisperse adsorbability composition of several natural and synthetic organic matrices. J. Colloid Interface Sci. 265(2), 265-275], we demonstrated that the isotherm equation derived herein yields predictions that agree with the much more complicated fictive component-ideal adsorbed solution theory (IAST)-based model for NOM from different sources and over a range of initial concentrations.

Simplification of the IAST for activated carbon adsorption of trace organic compounds from natural water.

Recent studies have shown that the ideal adsorbed solution theory (IAST) coupled with the concept of equivalent background compound (EBC) can be simplified for describing trace organic compound adsorption from natural water, provided that the adsorbent surface loading is dominated by competing natural organic matter. The resulting simplified IAST has been used to reduce the complexity of kinetic models for various dynamic adsorption processes. In order to be correctly applied, however, the simplified IAST requires some additional clarification and a quantitative evaluation of the deviation caused by the simplifying assumption. In this study, we derive a simple equation that relates the relative deviation of the simplified IAST directly to the molar ratio of EBC and trace organic compound surface loadings and their Freundlich isotherm exponents. We then verify the simplified IAST using the original IAST and experimental isotherm data from the literature for trace organic compounds at various initial concentrations in natural water. By further assuming that the adsorbed amount of the EBC is substantially greater than what remains in solution, a new pseudo single-solute isotherm equation is derived and a simple relation is subsequently established between the carbon dose and the remaining trace compound concentration. The results show that the adsorption capacity and relative removal of a trace organic compound at any carbon dose can be estimated directly with the simple equations developed here and data from a single isotherm experiment for the target compound conducted in the natural water of interest.

Application of a three-component competitive adsorption model to evaluate and optimize granular activated carbon systems.

A recently developed kinetic model for granular activated carbon (GAC) adsorbers (COMPSORB-GAC) that quantitatively describes the adsorption of trace organic contaminant in the presence of competing natural organic matter (NOM) was applied to evaluate the performance of different GAC system configurations: conventional fixed-bed adsorbers, layered upflow carbon adsorbers (LUCA), and moving-bed adsorbers (with few or many bed sections). COMPSORB-GAC separately tracks the adsorption of three components: a trace compound, a strongly competing NOM fraction that reduces trace compound equilibrium capacity, and a pore-blocking NOM fraction that reduces kinetics. Performance was simulated for various design criteria and with model parameters derived for two natural waters with significantly different NOM concentrations. For the range of simulated conditions and with baseline performance defined by a fixed-bed adsorber, LUCA generally reduced carbon usage rates (CURs) by 15-35%. A 2-section and a 16-section moving-bed reactor reduced baseline CURs by 20-30% and 45-55%, respectively. Projected CURs for the water source with a relatively high NOM concentration were 2-3 times higher for all reactor configurations and indicated that NOM preloading would cause performance deterioration in deep GAC beds, which highlights the importance of source water quality. These results show how COMPSORB-GAC can be used in a comprehensive, site-specific optimization of GAC systems to ensure robust system performance and to balance capital and operating costs.

Utilizing ion-exchange resin to improve recovery from organic shock-loading in an AnMBR treating sewage sludge.

The addition of ion-exchange resin in a two-phase continuous AnMBR system treating primary sludge at ambient temperature (20 °C) was investigated as a means to improve reactor recovery after organic shock-loading. Four commercially available anion-exchange resins were evaluated for their ability to sorb soluble organics, specifically volatile fatty acids (VFA), from AnMBR effluent. The strong-base resin, Purolite TANEX, was determined the best resin for deployment in the continuous AnMBR having achieved the greatest removal of soluble chemical oxygen demand (sCOD) (up to 36%) and acetic acid (up to 48%) in preliminary batch testing. Addition of 100 and 300 g/L TANEX in the AnMBR system improved effluent quality reducing effluent COD concentrations by 48 and 75%, respectively, under normal operating conditions. After shock-loading with 16,000 mg COD/L as acetic acid, reactor recovery in terms of methane production was 9-58% faster with the addition of TANEX than without, under controlled pH conditions (pH: 7.4). After shock-loading the system twice without the addition of TANEX it was found that recovery improved by 19% suggesting that acclimation of the microbial community also played a role in reactor recovery. Microbial community analysis using 16 S Illumina MiSeq sequencing confirmed changes in the microbial community did occur in response to shock-loading, with higher relative abundance of Methanoscarcina in the majority of post-shock-load microbial communities. The highest relative abundance of Methanoscarcina (51-58%) was seen during operating periods with the addition of TANEX resin, leading to the conclusion that addition of the TANEX resin benefited reactor recovery by serving as a temporary physio-chemical sink for the excess acetic acid, allowing the microbial community time to adjust to their new environmental conditions and become better able to process the higher levels of acetic acid associated with the organic shock.

Chemical characterization and anaerobic biodegradability of hydrothermal liquefaction aqueous products from mixed-culture wastewater algae.

This study examined the chemical characteristics and the anaerobic degradability of the aqueous product from hydrothermal liquefaction (HTL-ap) from the conversion of mixed-culture algal biomass grown in a wastewater treatment system. The effects of the HTL reaction times from 0 to 1.5 h, and reaction temperatures from 260 °C to 320 °C on the anaerobic degradability of the HTL-ap were quantified using biomethane potential assays. Comparing chemical oxygen demand data for HTL-ap from different operating conditions, indicated that organic matter may partition from organic phase to aqueous phase at 320 °C. Moderate lag phase and the highest cumulative methane production were observed when HTL-ap was obtained at 320 °C. The longest lag phase and the smallest production rate were observed in the process fed with HTL-ap obtained at 300 °C. Nevertheless, after overcoming adaptation issues, this HTL-ap led to the second highest accumulated specific methane production. Acetogenesis was identified as a possible rate-limiting pathway.

Improving anaerobic digestion of a cellulosic waste via routine bioaugmentation with cellulolytic microorganisms.

This study investigated routine bioaugmentation in the acid-phase of a two-phase anaerobic digestion (AD) process treating a largely cellulosic waste material generated from sweet corn processing. A proprietary cellulolytic bioculture was used for bioaugmentation with the aim of increasing substrate hydrolysis to improve overall methanogenic efficiency. In a sequencing batch experiment routine bioaugmentation achieved significantly greater soluble chemical oxygen demand (sCOD) generation (+25%) and methane production (+15%) compared to one-time bioaugmentation. In a continuous bench-scale system, routine bioaugmentation increased acid-phase sCOD by 29-68% and acetic acid concentrations by 31-34%. This benefit to hydrolysis and acetogenesis subsequently led to sustained increase in methane production (+56%) compared to non-bioaugmentation. A cursory economic analysis indicated that routine bioaugmentation could improve the economics of corn waste AD by $27-$34/dry tonne of waste. Overall, routine bioaugmentation showed significant promise for improving AD of corn waste by achieving sustained increases in substrate hydrolysis and methane production.

Characterization of aqueous phase from the hydrothermal liquefaction of Chlorella pyrenoidosa.

This study investigated the characteristics of aqueous phase from hydrothermal liquefaction of low-lipid microalgae Chlorella pyrenoidosa. The interactions of operating conditions, including reaction temperature, retention time and total solid ratio were evaluated by response surface methodology. The chemical oxygen demand, total nitrogen and total phosphorus were selected as indicators of the property of AP. Results indicated that total solid ratio was found to be the dominant factor affecting the nutrient recovery efficiencies of AP. Based on energy recovery, GC-MS indicated that the AP at two optimized operating conditions (280 °C, 60 min, 35 wt.% and 300 °C, 60 min, 25 wt.%) were observed to have a higher concentration of organic acids (10.35% and 8.34%) while the sample (260 °C, 30 min, 35 wt.%) was observed to have the highest concentration of N&O-heterocyclic compounds (36.16%).

Hydrothermal liquefaction of mixed-culture algal biomass from wastewater treatment system into bio-crude oil.

In this study, a mixed-culture algal biomass harvested from a functioning wastewater treatment system (AW) was hydrothermally converted into bio-crude oils. The highest bio-crude oil yield (49% of volatile matter) and the highest energy recovery were obtained at 300 °C with 1 h retention time. The highest heating value of the bio-crude oil was 33.3 MJ/kg, produced at 320 °C and 1h retention time. Thermogravimetric analysis showed approximately 60% of the bio-crude oils were distilled in the range of 200-550 °C; and the solid residue might be suitable for use in asphalt. GC-MS results indicated that the bio-crude oil contained hydrocarbons and fatty acids, while the aqueous product was rich in organic acids and cyclic amines. The nitrogen recovery (NR) in the bio-crude oil ranged from 8.41% to 16.8%, which was lower than the typical range of 25%-53% from previous studies.

Algal cell disruption using microbubbles to localize ultrasonic energy.

Microbubbles were added to an algal solution with the goal of improving cell disruption efficiency and the net energy balance for algal biofuel production. Experimental results showed that disruption increases with increasing peak rarefaction ultrasound pressure over the range studied: 1.90 to 3.07 MPa. Additionally, ultrasound cell disruption increased by up to 58% by adding microbubbles, with peak disruption occurring in the range of 10(8)microbubbles/ml. The localization of energy in space and time provided by the bubbles improve efficiency: energy requirements for such a process were estimated to be one-fourth of the available heat of combustion of algal biomass and one-fifth of currently used cell disruption methods. This increase in energy efficiency could make microbubble enhanced ultrasound viable for bioenergy applications and is expected to integrate well with current cell harvesting methods based upon dissolved air flotation.

Characterization of microalgae-bacteria consortium cultured in landfill leachate for carbon fixation and lipid production.

The characteristics of cultivating high-density microalgae-bacteria consortium with landfill leachate was tested in this study. Landfill leachate was collected from Laogang landfill operated for over 10 years in Shanghai, China. The maximum biomass concentration of 1.58g L(-1) and chlorophyll a level of 22mg L(-1) were obtained in 10% leachate spike ratio. Meanwhile, up to 90% of the total nitrogen in landfill leachate was removed in culture with 10% leachate spike ratio with a total nitrogen concentration of 221.6mg L(-1). The fluorescence peak of humic-like organic matters red shifted to longer wavelengths by the end of culture, indicating that microalgae-bacteria consortium was effective for treating landfill leachate contaminants. Furthermore, with the leachate spike ratio of 10%, the maximum lipid productivity and carbon fixation were 24.1 and 65.8mg L(-1)d(-1), respectively. Results of this research provide valuable information for optimizing microalgae culture in landfill leachate.

Effects of hydrothermal liquefaction on the fate of bioactive contaminants in manure and algal feedstocks.

This study investigated the effects of hydrothermal liquefaction (HTL) on the fate of bioactive compounds (BACs) often present with wet biosolids from wastewater, manure, or algae. Tracking radiolabeled (14)C for two BACs showed that 60-79% of the carbon was transferred to the HTL raw oil product, and most of the rest was found in the aqueous product. In the presence of both swine manure and Spirulina biomass feedstocks, HTL provided essentially complete removal of three BACs when operated at 300°C for ≥ 30 min. Experiments with both natural transformation and high-efficiency transformation showed that HTL provided complete deactivation of antibiotic resistant genes for all tested HTL conditions (250-300°C, 15-60 min reaction time). Thus, incorporating HTL into wastewater treatment systems can simultaneously produce valuable bio-crude oil, provide effective removal of BACs and disrupt the natural pathways for antibiotic resistant gene transfer from manure and wastewater biosolids to the environment.

Chemical properties of biocrude oil from the hydrothermal liquefaction of Spirulina algae, swine manure, and digested anaerobic sludge.

This study explores the influence of wastewater feedstock composition on hydrothermal liquefaction (HTL) biocrude oil properties and physico-chemical characteristics. Spirulina algae, swine manure, and digested sludge were converted under HTL conditions (300°C, 10-12 MPa, and 30 min reaction time). Biocrude yields ranged from 9.4% (digested sludge) to 32.6% (Spirulina). Although similar higher heating values (32.0-34.7 MJ/kg) were estimated for all product oils, more detailed characterization revealed significant differences in biocrude chemistry. Feedstock composition influenced the individual compounds identified as well as the biocrude functional group chemistry. Molecular weights tracked with obdurate carbohydrate content and followed the order of Spirulina

Three-component adsorption modeling to evaluate and improve integrated sorption-membrane processes.

Integrated sorption-membrane (ISM) processes combining low-pressure membranes with adsorbents are increasingly popular because they cost-effectively expand low-pressure membrane treatment to include dissolved contaminant removal. However, contemporary ISM processes often exhibit antagonistic tradeoffs between adsorption and membrane performance that were investigated using state-of-the-art adsorption models that include both of the predominant competitive effects of natural organic matter: direct site competition and pore blockage. Two currently used ISM process configurations, powdered activated carbon-ultrafiltration (PAC-UF) and adsorptive floc blanket reactor-ultrafiltration (FBR-UF), were compared with a novel configuration, upflow adsorption-ultrafiltration (UA-UF), which consists of a moving-bed of granular activated carbon upstream of a membrane. Model simulations quantitatively compared performance and evaluated potential improvements for each configuration. For instance, using contemporary PAC-UF practices and 90% atrazine removal as a baseline, alternative membrane backwashing procedures can lower carbon usage rates (CURs) by 75% but may also reduce membrane hydraulic performance. Using the same baseline, FBR-UF can reduce CURs by 92% while simultaneously improving membrane performance via pretreatment; however, process size increases 10-fold. The novel UA-UF configuration only increases process size modestly, but can still yield CURs 96% lower than the PAC-UF baseline while simultaneously providing beneficial membrane pretreatment and improving sustainability features by reducing residuals.

Competitive effects of natural organic matter: parametrization and verification of the three-component adsorption model COMPSORB.

Natural organic matter (NOM) hinders adsorption of trace organic compounds on powdered activated carbon (PAC) via two dominant mechanisms: direct site competition and pore blockage. COMPSORB, a three-component model that incorporates these two competitive mechanisms, was developed in a previous study to describe the removal of trace contaminants in continuous-flow hybrid PAC adsorption/membrane filtration systems. Synthetic solutions containing two model compounds as surrogates for NOM were used in the original study to elucidate competitive effects and to verify the model. In the present study, a quantitative method to characterize the components of NOM that are responsible for competitive adsorption effects in natural water was developed to extend the application of COMPSORB to natural water systems. Using batch adsorption data, NOM was differentiated into two fictive fractions, representing the strongly competing and pore blocking components, and each was treated as a single compound. The equilibrium and kinetic parameters for these fictive compounds were calculated using simplified adsorption models. This parametrization procedure was carried out on two different natural waters, and the model was verified with experimental data obtained for atrazine removal from natural water in a PAC/membrane system. The model predicted the system performance reasonably well and highlighted the importance of considering both direct site competition and pore blockage effects of NOM in modeling these systems.

Three-component competitive adsorption model for fixed-bed and moving-bed granular activated carbon adsorbers. Part I. Model development.

Heterogeneous natural organic matter (NOM) present in all natural waters impedes trace organic contaminant adsorption, and predictive modeling of granular activated carbon (GAC) adsorber performance is often compromised by inadequate accounting forthese competitive effects. Thus, a 3-component adsorption model, COMPSORB-GAC, is developed that separately tracks NOM adsorption and its competitive effects as a function of NOM surface loading. In this model, NOM is simplified into two fictive fractions with distinct competitive effects on trace compound adsorption: a smaller, strongly competing fraction that reduces equilibrium capacity and a larger pore-blocking fraction that reduces adsorption kinetics (both external film mass transfer and surface diffusion). COMPSORB-GAC tracks these two NOM fractions, along with the trace compound, and changes adsorption parameters according to the local surface loading of the two NOM fractions. Model parameters are allowed to vary both temporally and spatially to reflect differences in the NOM preloading conditions that occur in GAC columns. This dual-resistance model is based on homogeneous surface diffusion with external film mass-transfer limitations. The governing equations are expressed in a moving-grid finite-difference formulation to accommodate the modeling of spatially varying parameters and moving-bed reactors with counter-current adsorbent flow. A series of short-term adsorption tests with fresh and preloaded GAC is proposed to determine the necessary model input parameters. The accompanying manuscript demonstrates the parameterization procedure and verifies the model with experimental data.