Environmental life cycle assessment of treatment and management strategies for food waste and sewage sludge.

A consequential life cycle assessment (LCA) was utilized to compare the environmental impacts of food waste and sewage sludge management strategies. The strategies included a novel two-phase anaerobic digestion (AD) system and alternatives including landfill, waste-to-energy, composting, anaerobic membrane bioreactor, and conventional AD (wet continuous stirred-tank reactor [CSTR]). The co-management of food waste with sewage sludge was also considered for the two-phase AD system and for a conventional AD reactor. A multidimensional LCA approach was taken, considering the five-midpoint impact categories of global warming, smog, human health particulate, acidification, and eutrophication estimated using the U.S. EPA Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts. Co-management of food waste and sewage sludge using the novel two-phase AD system was shown to maximize energy recovery and had a net global warming benefit while reducing other environmental impacts compared with the alternative management strategies. It had similar relative environmental advantages across all categories as conventional AD, with the advantage of a smaller physical footprint. However, both approaches featured net environmental burdens when the background electric grid intensity fell below 0.25 kg CO2-eq kWh-1, as could be expected in a decarbonized electric future. Upgrading the biogas produced from AD to renewable natural gas can displace the use of fossil natural gas for other non-electricity energy requirements that are difficult to decarbonize and may extend the time period of significant environmental benefits of utilizing AD for organic waste management. Treatment of the nutrient-rich supernatant generated by the novel two-phase AD system could be an obstacle for utilities with stringent nutrient discharge limits. Future research and full-scale implementation are needed to demonstrate the benefits of the two-phase AD system predicted through this analysis.

Installing Controlled Stereo-Defects Yields Semicrystalline and Biodegradable Poly(3-Hydroxybutyrate) with High Toughness and Optical Clarity.

Stereo-defects present in stereo-regular polymers often diminish thermal and mechanical properties, and hence suppressing or eliminating them is a major aspirational goal for achieving polymers with optimal or enhanced properties. Here, we accomplish the opposite by introducing controlled stereo-defects to semicrystalline biodegradable poly(3-hydroxybutyrate) (P3HB), which offers an attractive biodegradable alternative to semicrystalline isotactic polypropylene but is brittle and opaque. We enhance the specific properties and mechanical performance of P3HB by drastically toughening it and also rendering it with the desired optical clarity while maintaining its biodegradability and crystallinity. This toughening strategy of stereo-microstructural engineering without changing the chemical compositions also departs from the conventional approach of toughening P3HB through copolymerization that increases chemical complexity, suppresses crystallization in the resulting copolymers, and is thus undesirable in the context of polymer recycling and performance. More specifically, syndio-rich P3HB (sr-P3HB), readily synthesized from the eight-membered meso-dimethyl diolide, has a unique set of stereo-microstructures comprising enriched syndiotactic [rr] and no isotactic [mm] triads but abundant stereo-defects randomly distributed along the chain. This sr-P3HB material is characterized by high toughness (UT = 96 MJ/m3) as a result of its high elongation at break (>400%) and tensile strength (34 MPa), crystallinity (Tm = 114 °C), optical clarity (due to its submicron spherulites), and good barrier properties, while it still biodegrades in freshwater and soil.

Microbial communities for valorizing biomass using the carboxylate platform to produce volatile fatty acids: A review.

The carboxylate platform employs a diverse microbial consortium of anaerobes in which the methanogens are inhibited. Nearly all biomass components are digested to a mixture of C1-C8 monocarboxylic acids and their corresponding salts. The methane-arrested anaerobic digestion proceeds readily without needing to sterilize biomass or equipment. It accepts a wide range of feedstocks (e.g., agricultural residues, municipal solid waste, sewage sludge, animal manure, food waste, algae, and energy crops), and produces high product yields. This review highlights several important aspects of the platform, including its thermodynamic underpinnings, influences of inoculum source and operating conditions on product formation, and downstream chemical processes that convert the carboxylates to hydrocarbon fuels and oxygenated chemicals. This review further establishes the carboxylate platform as a viable and economical route to industrial biomass utilization.

Arrested methanogenesis digestion of high-strength cheese whey and brewery wastewater with carboxylic acid production.

A new anaerobic digestion process based on arrested methanogenesis (AM) was developed to treat high-strength cheese whey and brewery wastewater with simultaneous carboxylic acid production. This study specifically determined the links between wastewater characteristics, microbial community structure, and the operation of AM digesters at the bench scale. The highest total carboxylic acids concentration (78 g/L) was achieved after 15 days under batch condition at 40 °C and near-neutral pH. Lactate conversion to chain-elongated volatile fatty acid was observed. Under fed-batch conditions, the highest total acid productivity was 16 g/(Lliq·d) with substrate conversion of 0.66 g CODdigested/g CODfed at hydraulic residence time (HRT) of 4 days. Fed-batch digestion with biomass recycling resulted in a 2-fold increase in VFAs concentration (30 g/L) and a higher diversity in the microbial consortia. Experimental results show that highly efficient, robust, and productive community structure was established for sustainable carboxylate production from widely varying high-strength wastewaters.

Electricity from lignocellulosic substrates by thermophilic Geobacillus species.

Given our vast lignocellulosic biomass reserves and the difficulty in bioprocessing them without expensive pretreatment and fuel separation steps, the conversion of lignocellulosic biomass directly into electricity would be beneficial. Here we report the previously unexplored capabilities of thermophilic Geobacillus sp. strain WSUCF1 to generate electricity directly from such complex substrates in microbial fuel cells. This process obviates the need for exogenous enzymes and redox mediator supplements. Cyclic voltammetry and chromatography studies revealed the electrochemical signatures of riboflavin molecules that reflect mediated electron transfer capabilities of strain WSUCF1. Proteomics and genomics analysis corroborated that WSUCF1 biofilms uses type-II NADH dehydrogenase and demethylmenaquinone methyltransferase to transfer the electrons to conducting anode via the redox active pheromone lipoproteins localized at the cell membrane.

In-situ biogas upgrading during anaerobic digestion of food waste amended with walnut shell biochar at bench scale.

A modified version of an in-situ CO2 removal process was applied during anaerobic digestion of food waste with two types of walnut shell biochar at bench scale under batch operating mode. Compared with the coarse walnut shell biochar, the fine walnut shell biochar has a higher ash content (43 vs. 36 wt%) and higher concentrations of calcium (31 vs. 19 wt% of ash), magnesium (8.4 vs. 5.6 wt% of ash) and sodium (23.4 vs. 0.3 wt% of ash), but a lower potassium concentration (0.2 vs. 40% wt% of ash). The 0.96-3.83 g biochar (g VSadded)-1 fine walnut shell biochar amended digesters produced biogas with 77.5%-98.1% CH4 content by removing 40%-96% of the CO2 compared with the control digesters at mesophilic and thermophilic temperature conditions. In a direct comparison at 1.83 g biochar (g VSadded)-1, the fine walnut shell biochar amended digesters (85.7% CH4 content and 61% CO2 removal) outperformed the coarse walnut shell biochar amended digesters (78.9% CH4 content and 51% CO2 removal). Biochar addition also increased alkalinity as CaCO3 from 2800 mg L-1 in the control digesters to 4800-6800 mg L-1, providing process stability for food waste anaerobic digestion.

Printing-Assisted Surface Modifications of Patterned Ultrafiltration Membranes.

Understanding and restricting microbial surface attachment will enhance wastewater treatment with membranes. We report a maskless lithographic patterning technique for the generation of patterned polymer coatings on ultrafiltration membranes. Polyethylene glycol, zwitterionic, or negatively charged hydrophilic polymer compositions in parallel- or perpendicular-striped patterns with respect to feed flow were evaluated using wastewater. Membrane fouling was dependent on the orientation and chemical composition of the coatings. Modifications reduced alpha diversity in the attached microbial community (Shannon indices decreased from 2.63 to 1.89) which nevertheless increased with filtration time. Sphingomonas species, which condition membrane surfaces and facilitate cellular adhesion, were depleted in all modified membranes. Microbial community structure was significantly different between control, different patterns, and different chemistries. This study broadens the tools for surface modification of membranes with polymer coatings and for understanding and optimization of antifouling surfaces.

Achieving the Great Lakes Initiative mercury limits in oil refinery effluent.

To meet the stringent Great Lakes Initiative (GLI) wastewater discharge mercury (Hg) limit of 1.3 ppt (ng/L), mercury removal technologies need to be identified and investigated. The goals of this study were to (1) identify and assess available wastewater treatment technologies for mercury removal from an oil refinery wastewater; and (2) conduct bench-scale tests to provide comparable, transparent, and uniform results to assess their performance at low mercury concentrations. The study found that many tested technologies were able to achieve the GLI mercury target concentration at the bench-scale, albeit with different efficiencies and engineering implications. These results demonstrate that at this scale there is no fundamental physical or chemical barrier to achieving < 1.3 ng Hg/L in the tested wastewater. The study also found that some technologies were effective on particulate mercury whereas others were effective on dissolved mercury. One emerging treatment technology was found to be effective on both particulate and dissolved mercury. Three mercury-removal technologies--ultrafiltration (particulate mercury), adsorption (dissolved mercury), and an emerging reactive filtration technology (particulate and dissolved mercury)--are recommended for further study. This research offers treatment alternatives for different forms of mercury in an oil refinery wastewater, which might be applicable to other types of mercury-containing wastewater.

Meeting world's most stringent Hg criterion: a pilot-study for the treatment of oil refinery wastewater using an ultrafiltration membrane process.

A membrane ultrafiltration (UF) technology was tested using an oil refinery's end-of-pipe effluent to demonstrate the proof of concept, i.e. can the Great Lakes Initiative criterion of less than 1.3 ppt be consistently met at the pilot-scale, and to provide the data necessary for preliminary full-scale process design. This study presents the successful pilot test conducted with continuous but varying feed conditions over a protracted period. The UF membrane process consistently provided a constant permeate quality at all tested operating conditions, virtually independent of the feed water characteristics and the feed Hg concentration (0.5-22.7 ppt). The treatment target of less than 1.3 ppt of Hg was met and exceeded for all tested conditions during the pilot study. Turbidity measurements were <0.5 NTU (with a MDL of 0.5 NTU) 85% of the time and <0.16 NTU 95% of the time when analyzed on-line. The TMP values were below the specification of (negative) 7-12 psi at all tested conditions during the pilot-study. Weekly maintenance cleans and monthly clean in place (CIP) events were very effective in consistently restoring the membrane permeability during the pilot-study.

Achieving very low mercury levels in refinery wastewater by membrane filtration.

Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes were evaluated for their ability to achieve the world's most stringent Hg discharge criterion (<1.3ng/L) in an oil refinery's wastewater. The membrane processes were operated at three different pressures to demonstrate the potential for each membrane technology to achieve the targeted effluent mercury concentrations. The presence of mercury in the particulate form in the refinery wastewater makes the use of MF and UF membrane technologies more attractive in achieving very low mercury levels in the treated wastewater. Both NF and RO were also able to meet the target mercury concentration at lower operating pressures (20.7bar). However, higher operating pressures (≥34.5bar) had a significant effect on NF and RO flux and fouling rates, as well as on permeate quality. SEM images of the membranes showed that pore blockage and narrowing were the dominant fouling mechanisms for the MF membrane while surface coverage was the dominant fouling mechanism for the other membranes. The correlation between mercury concentration and particle size distribution was also investigated to understand mercury removal mechanisms by membrane filtration. The mean particle diameter decreased with filtration from 1.1±0.0µm to 0.74±0.2µm after UF.

Improving data quality on low level mercury wastewater analysis.

In order to compare treatability test results evaluating low-level mercury (Hg) removal from oil refinery wastewater, improvements in Hg analytical methods were conducted at two US EPA certified analytical labs. The revisions in the analytical protocols improved Hg recoveries and hence enabled more reliable data interpretation and comparison for the specific wastewater tested. Nevertheless, significant differences between results from the two laboratories were identified in a split-sample experiment.

Role of hemoglobin in improving biodegradation of aromatic contaminants under hypoxic conditions.

Genetic engineering of bacteria using the Vitreoscilla (bacterial) hemoglobin gene has been used to enhance bioremediation of several compounds which are models for, or are themselves, toxic chemicals which may contaminate soil and water. Initial experiments, done mostly in shake flasks, with Escherichia coli, Burkholderia sp. DNT and Pseudomonas aeruginosa demonstrated that expression of Vitreoscilla hemoglobin in heterologous hosts can enhance biodegradation of several aromatic compounds as well as an organophosphorus compound. These studies concentrated for the most part on enhancement of endogenous catabolic capabilities of the hosts; the presence of vgb/VHb enhanced both growth and biodegradation. The initial studies were followed by experiments in systems which more closely approximated conditions that would exist in field applications. These included soil columns, continuous flow reactors and membrane bioreactors. The latter work also enabled calculation of the effects of the presence of vgb/VHb on kinetic parameters such as growth rate, substrate and oxygen utilization rate, and degradation rate of pollutants, etc. Although not always the case, for the most part, and particularly in bioreactors, the advantages due to vgb/VHb were greater under conditions of limited aeration or hypoxic conditions.

Bioavailability of dissolved organic nitrogen in treated effluents.

The research objective was to assess dissolved organic nitrogen (DON) bioavailability in wastewater effluents from a pilot-scale nitrification plant and a laboratory-scale total nitrogen (TN) removal plant. The DON bioavailability was assessed using a 14-day bioassay protocol containing bacterial and algal inocula. Nitrogen species, dissolved organic carbon, chlorophyll a, and biomass (as total suspended solids and culturable cell counts) concentrations were measured to assess DON bioavailability. The results showed an increase in algal chlorophyll a concentration, with a concurrent increase in algal biomass over time; increased bacterial counts and a decrease in DON concentration over time; and increased carbon-to-nitrogen ratio at the end of the 14-day bioassay, indicating effluent DON bioavailability to algae and bacteria. Approximately 18 to 61% of the initial DON in low-total-nitrogen wastewater effluent (TN = 4 to 5 mg/L) sample was bioavailable. The results show that bacteria and algae uptake and release DON during their growth.

Aerobic membrane bioreactor for ammonium-rich wastewater treatment.

The major research objective involving ammonia-rich synthetic wastewater (centrate) treatment using a membrane bioreactor (MBR) was to determine the suitable hydraulic retention time (HRT), solids retention time (SRT), and ammonium loading rate for complete nitrification of centrate. The experiments were performed using a laboratory-scale 2-L MBR, which was supplied with synthetic wastewater (1000 mg nitrogen/L and 350 mg chemical oxygen demand [COD]/L). The entire study period was divided into five different experimental runs based on various HRTs and SRTs. Batch nitrification rate tests and microbial studies using fluorescent in situ hybridization were also conducted. The MBR was able to achieve more than 95% ammonium removal efficiency and 90% carbonaceous soluble COD removal efficiency. The experimental results showed that complete nitrification of centrate during treatment can be achieved at a 1-day HRT and 50-day SRT. The suitable ammonium loading rate was found to be 0.3 mg nitrogen/mg volatile suspended solids/d.

Comparison of 2-chlorobenzoic acid biodegradation in a membrane bioreactor by B. cepacia and B. cepacia bearing the bacterial hemoglobin gene.

Degradation of 2-chlorobenzoic acid (2-CBA), a model recalcitrant chlorinated organic compound, by pure cultures of Burkholderia cepacia strain DNT with (transformed B. cepacia) and without (untransformed B. cepacia) the bacterial hemoglobin (Vitreoscilla hemoglobin, VHb) gene, vgb, was investigated in parallel membrane bioreactors (MBRs). This was done aseptically to prevent contamination during the operation of the MBRs. The objective was to determine whether the degradation of 2-CBA by cometabolism, using acetate as a primary carbon source, under hypoxic conditions might be enhanced for vgb-bearing cells in MBRs. The 2-CBA removal efficiency of transformed B. cepacia (97-99%) was slightly higher than that of untransformed B. cepacia (95-99%) at all stages. The average amount of chloride released from 2-CBA by transformed cells was also higher than for untransformed cells, 92-96% compared to 64-84% of the maximum theoretical amount, the exact value depending on the operating conditions. These results indicate that 2-CBA degradation/transformation is not accompanied by the stoichiometric release of chloride for the untransformed strain. The difference between percentages of 2-CBA removal and chloride release by untransformed cells was attributed to persistence, under hypoxic conditions, of the 2-CBA chlorine atom in 2-CBA metabolites. Growth of transformed cells was also significantly enhanced under hypoxic conditions compared to untransformed cells. For varying media compositions, the transformed cells reached higher cell densities (3.2-5.4 g/L) relative to untransformed cells (2.8-4.7 g/L) at food to microorganism ratios ranging from 0.44-0.59 to 0.38-0.49 g COD/g biomass-d The observed yields thus ranged from 0.16-0.20 and 0.15-0.18 g TSS/g COD for untransformed and transformed cells, respectively. The value of the yield depended on medium composition. The MBR system using vgb-containing B. cepacia maintained a high biomass concentration without oxygen limitations and provided cell-free effluent. Hence, it may be useful for treating high volumes of water contaminated with low levels of recalcitrant organics.

Use of genetically engineered microorganisms (GEMs) for the bioremediation of contaminants.

This paper presents a critical review of the literature on the application of genetically engineered microorganisms (GEMs) in bioremediation. The important aspects of using GEMs in bioremediation, such as development of novel strains with desirable properties through pathway construction and the modification of enzyme specificity and affinity, are discussed in detail. Particular attention is given to the genetic engineering of bacteria using bacterial hemoglobin (VHb) for the treatment of aromatic organic compounds under hypoxic conditions. The application of VHb technology may advance treatment of contaminated sites, where oxygen availability limits the growth of aerobic bioremediating bacteria, as well as the functioning of oxygenases required for mineralization of many organic pollutants. Despite the many advantages of GEMs, there are still concerns that their introduction into polluted sites to enhance bioremediation may have adverse environmental effects, such as gene transfer. The extent of horizontal gene transfer from GEMs in the environment, compared to that of native organisms including benefits regarding bacterial bioremediation that may occur as a result of such transfer, is discussed. Recent advances in tracking methods and containment strategies for GEMs, including several biological systems that have been developed to detect the fate of GEMs in the environment, are also summarized in this review. Critical research questions pertaining to the development and implementation of GEMs for enhanced bioremediation have been identified and posed for possible future research.

Enhanced electrokinetic dissolution of naphthalene and 2,4-DNT from contaminated soils.

Electrokinetic soil remediation has been proven to remove heavy metals and polar organics from low hydraulic conductivity subsurface environment. In this study, carboxymethyl-beta-cyclodextrin (CMCD) was used as a carrier to assist electrokinetic treatment for removal of low polarity organic contaminants from soils (2.2% organic carbon content). Naphthalene and 2,4-dinitrotoluene (2,4-DNT) were selected as the test compounds. The results from columns experiments showed that 46 and 43% of naphthalene and 2,4-DNT, respectively, were removed using 0.01 N NaNO(3) flushing solution with 40 V electrical potential while 70 and 72% of naphthalene and 2,4-DNT were removed using 2 g/L CMCD solution. Naphthalene and 2,4-DNT removal was enhanced to 83 and 89%, respectively, by using 2 g/L CMCD with 40 V electrical potential. Findings from this study also demonstrated that cyclodextrin assisted electrokinetics can enhance the removal rate of naphthalene and 2,4-DNT. Electric potential applied has more influence on the contaminant removal than the amount of CMCD used. Higher voltage application caused increase in the removal rate of naphthalene and 2,4-DNT, and appeared to be one of the critical factors in obtaining higher contaminant removal while increasing CMCD solution concentration above 2 g/L appeared to have little effect on the contaminant removal.

2-Chlorobenzoate biodegradation by recombinant Burkholderia cepacia under hypoxic conditions in a membrane bioreactor.

The feasibility of applying bacterial hemoglobin technology to degrade 2-chlorobenzoate (2-CBA) through co-metabolism under hypoxic conditions in a membrane bioreactor (MBR) process has been studied in the laboratory. 2-chlorobenzoate removal and chloride release rates in the MBR system varied from 99 to 78% and 98 to 73%, respectively, depending on the operation conditions. Chemical oxygen demand (COD) removal efficiencies were more than 90% at food-to-microorganism ratios ranging from 0.32 to 0.62 g/g/d, and the observed yield was 0.13 to 0.20 g biomass/g COD. The bacterial cell-floc size-distribution analysis showed that there is a significant change in bacterial floc size due to high shear stress during operation of the MBR. To characterize growth kinetics of Burkholderia cepacia strain dinitrotoluene, a mathematical model that describes co-metabolic oxidation of 2-CBA in an MBR has been developed.

Enhanced kinetics of genetically engineered Burkholderia cepacia: the role of vgb in the hypoxic metabolism of 2-CBA.

Application of Vitreoscilla hemoglobin (VHb) technology to 2-CBA degradation by Burkholderia cepacia strain DNT under hypoxic conditions was studied in continuous culture chemostats. Dechlorination abilities of both recombinant (VHb gene (vgb) containing) and untransformed cells were investigated at various dilution rates to ensure complete degradation of 2-CBA. As the dilution rate increased from 0.025 to 0.25 h(-1), the ratios of chloride release to degraded 2-CBA concentration decreased from 0.95 to 0.72 and from 0.89 to 0.39 for recombinant and untransformed cells, respectively. A nonstoichiometric relationship between chloride release and 2-CBA degradation was more pronounced for untransformed cells. Recombinant cell densities were 0.1-0.2. g L(-1) greater than untransformed cell densities for a range of dilution rates. As the dilution rate increased, the oxygen uptake rate (OUR) and the substrate utilization rate (SUR) decreased for both strains. The OUR/SUR ratio increased as the dilution rate increased for both strains but was much higher for the recombinant strain compared to untransformed cells. The specific 2-CBA degradation rate of recombinant cells was greater than that of untransformed cells (1.17 vs. 0.46 mg CBA (mg) day(-1), and half-saturation constants for recombinant cells were lower than those of untransformed cells (0.18 and 0.32 mg CBA L(-1), respectively). The pseudo-first-order degradation constants, k(1CBA) and k(1ACE), were higher for recombinant cells (6.5 L (mg cells)(-1) day(-1) and 95.6 L (mg cells)(-1) day(-1), respectively) than those of untransformed cells (1.44 L (mg cells)(-1) day(-1) and 73.7 L (mg cells)(-1) day(-1), respectively).

Biodegradation of 2-chlorobenzoate by recombinant Burkholderia cepacia expressing Vitreoscilla hemoglobin under variable levels of oxygen availability.

The influence of bacterial hemoglobin, VHb, on dechlorination and degradation of 2-chlorobenzoate (2-CBA) by recombinant Burkholderia sp. under variable oxygen availability with an initial dissolved oxygen concentration of 0.27 mM-0.72 mM was investigated in batch and continuous culture. Ability to express VHb was provided to recombinant Burkholderia by transformation with the VHb gene, vgb, on plasmid pSC160. 100% of 0.5 mM CBA was degraded in cultures with 85% and 70% of total volume as headspace air in closed reactors by both wild type and recombinant Burkholderia. The recombinant cultures were able to dechlorinate and degrade 100% of the 2-CBA in less than 48 hours at 30 degrees C compared to more than 120 hours for wild type cultures. The rate and extent of CBA degradation by recombinant cultures with 40% of total volume as headspace air was higher than those achieved by wild type cells at the end of the 168 hours of incubation period, 98 and 73%, respectively. The chloride released: CBA degraded molar ratio for cultures with 40% of total volume headspace air was nearly stoichiometric (molar ratio = 1.0) for recombinant strains, whereas it was non-stoichiometric (molar ratio = 0.24) for wild type cells. The results suggest a suicidal meta-pathway for wild type cells and a complete dechlorination and degradation pathway for recombinant cells under hypoxic conditions. The degradation and dechlorination ability of both types of cells was also investigated in continuous reactor studies by varying the dilution rate under hypoxic conditions. Regarding potential of the recombinant strain for 2-CBA degradation in either open ecosystems or closed bioreactor bioremediation systems, the stability of the plasmid containing vgb in the recombinant cells was also studied; the plasmid was 100% stable at 0.025 h(-1) dilution rate (approximately 1.7 d hydraulic retention time), even after one month.