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.

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.

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.

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.

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.

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.

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.

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.

Three-component competitive adsorption model for fixed-bed and moving-bed granular activated carbon adsorbers. Part II. Model parameterization and verification.

COMPSORB-GAC is a 3-component competitive adsorption kinetic model for granular activated carbon (GAC) adsorbers that was developed in Part I of this study, including a proposed procedure for determining model parameters in natural water applications with background natural organic matter (NOM). Part II of this study demonstrates the proposed parameterization procedure and validates the modeling approach by comparing predictions with experimental breakthrough curves at multiple empty-bed contact times for both fixed-bed and moving-bed reactors. The parameterization procedure consists of a set of independent, short-term experimental tests with fresh and batch preloaded adsorbents and then data fitting using both classic and recently developed theoretical expressions. The model and parameterization procedure simplifies NOM into two fictive fractions (pore-blocking and strongly competing) and incorporates three competitive effects that vary both temporally and axially in a GAC column (direct competition for sites, intraparticle pore blockage, and external surface pore blockage). With all three competitive mechanisms accounted for, the model could accurately predict breakthrough profiles for column lengths and durations that were much longer than those used for model parameterization. Model predictions that ignored one or more of the competitive mechanisms showed that each mechanism was important for different regions of the breakthrough curve. The external surface pore-blockage effect was predominant for the prediction of early breakthrough data, whereas direct competition for sites and intraparticle pore blockage were prevalent when predicting higher breakthrough levels and data later in the column run.

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.