Holistic biorefinery approach for biogas and hydrogen production: Integration of anaerobic digestion with hydrothermal carbonization and steam gasification.

Recently, the integration of biochemical and thermochemical processes is recognized as a promising strategy for the valorization of lignocellulosic biomass into renewable energy production. In this study, different routes for the valorization of hemp hurd for biohydrogen and biomethane production were proposed, including anaerobic digestion (AD), hydrothermal carbonization, and steam gasification. AD results revealed that NaOH pre-treatment of hemp hurd improved biomethane production yield by 164%. Comparing hydrochars from raw hemp, digestate derived hydrochars had higher mass yield due to changes in composition during AD as well as high ash content of digestates. It was found that high ash content of digestates originated from inorganic compounds in inoculum that accumulated over hemp hurd during anaerobic digestion process. Among feedstocks (hydrochars and raw hemp hurd), hemp hurd derived hydrochar at 200 °C showed the best performance in terms of H2 yield (1278 mL/g) whereas carbon efficiency reached % 92 in case of digestate derived hydrochar at 200 °C. HTC improved the steam gasification performance of hemp hurd whereas hydrochars from NaOH pretreated digestate yielded lowest hydrogen production due to the high content of inorganics, particularly phosphorus (P) and aluminum (Al). According to BMP test, spent liquor obtained at the lowest HTC temperature (200 °C) exhibited the highest BMP, reaching 213 mL CH4/g COD. Considering the overall gas products of four different routes, it is concluded that HTC as a post-treatment exhibits slightly better performance than HTC as pre-treatment. Although alkali pretreatment enhanced the anaerobic digestion performance, the resulting hydrochars exhibited low gasification activity.

Purified Terephthalic Acid Wastewater Treatment Using Modified Two-Stage UASB Bioreactor Systems.

Microbial community dynamics and PTA wastewater degradation performance of sequentially connected two-stage upflow anaerobic sludge blanket (UASB) bioreactors have been studied for 225 days. The working volume of acidogenic (R1) and methanogenic reactors (R2) have sixfold differences. Thus, the reactors operated under different hydraulic retention time (HRT) conditions, which are preferential for PTA wastewater content. Archeal and bacterial profiles of granules were analyzed with denaturing gradient gel electrophoresis (DGGE) and real-time quantitative PCR (Q-PCR) techniques. According to high-pressure liquid chromatography (HPLC) results, 4-Carboxybenzaldehyde (4-CBA) and acetic acid (AA) completely degraded in the first stage, whereas terephthalate (TA) and p-toluic acid (p-TA) degradation ratios were 90% and 47% in the second stage, respectively. The methane content of the UASB reactor was determined as 76% by gas chromatography (GC) analysis. Microbial community analysis indicated that the members of hydrogenotrophic methanogen groups Methanobacteriales and Methanomicrobiales were dominantly responsible for methane production throughout the process.

Bacterial and archeal dynamics of a labscale HYBRID gas fermentation bioreactor fed with CO2 and H2.

16s rDNA-based methods were used in order to identify the dynamics of microbial profiles in a HYBRID gas fermentation bio-methanization reactor. The effects of various H2 and CO2 ratios on microbial community were investigated. The HYBRID gas fermentation reactor was composed of granular anaerobic seed and the system fed with only H2 and CO2 gases. No additional organic material and trace element was fed during the throughout the experiments; thus, the microbial diversity was directly related to production of methane. The dynamics of the microbial communities were investigated with DGGE and real-time PCR analysis. The results showed that Methanobacteriales members were more dominated than Methanosarcinales and Methanomicrobiales members in the system. DGGE results indicated that Methanosaeta concilii, Methanoculleus sp., Methanosphaerula palustris, Methanofollis formosanus, Methanolinea sp., and Methanobacterium palustre were the most prominent methanogens depending on different H2/CO2 ratios. DGGE profiles suggested that hydrogenotrophic and acetoclastic species were responsible for the production of methane. The survival of syntrophic bacteria and acetoclastic methanogens was attributed to their utilization of organic materials provided by lysis. To the best of our knowledge, this is the first microbial profile detection study in a hybrid bioreactor system operated with only pure hydrogen and carbon dioxide.

Cell immobilization for microbial production of 1,3-propanediol.

Cell and enzyme immobilization are often used for industrial production of high-value products. In recent years, immobilization techniques have been applied to the production of value-added chemicals such as 1,3-Propanediol (1,3-PDO). Biotechnological fermentation is an attractive alternative to current 1,3-PDO production methods, which are primarily thermochemical processes, as it generates high volumetric yields of 1,3-PDO, is a much less energy intensive process, and generates lower amounts of environmental organic pollutants. Although several approaches including: batch, fed-batch, continuous-feed and two-step continuous-feed were tested in suspended systems, it has been well demonstrated that cell immobilization techniques can significantly enhance 1,3-PDO production and allow robust continuous production in smaller bioreactors. This review covers various immobilization methods and their application for 1,3-PDO production.

Experimental design methods for bioengineering applications.

Experimental design is a form of process analysis in which certain factors are selected to obtain the desired responses of interest. It may also be used for the determination of the effects of various independent factors on a dependent factor. The bioengineering discipline includes many different areas of scientific interest, and each study area is affected and governed by many different factors. Briefly analyzing the important factors and selecting an experimental design for optimization are very effective tools for the design of any bioprocess under question. This review summarizes experimental design methods that can be used to investigate various factors relating to bioengineering processes. The experimental methods generally used in bioengineering are as follows: full factorial design, fractional factorial design, Plackett-Burman design, Taguchi design, Box-Behnken design and central composite design. These design methods are briefly introduced, and then the application of these design methods to study different bioengineering processes is analyzed.

The effects of cell recycling on the production of 1,3-propanediol by Klebsiella pneumoniae.

The effects of both biomass age and cell recycling on the 1,3-propanediol (1,3-PDO) production by Klebsiella pneumoniae were investigated in a membrane-supported bioreactor using hollow-fiber ultrafiltration membrane module in two separate experiments. It was determined that older cells have a negative effect on 1,3-PDO production. The concentrations of by-products, such as acetic acid and ethanol, increased in cultures with older cells, whereas the concentrations of succinic acid, lactic acid and 2,3-butanediol decreased. The effect of cell recycling was comparatively studied at a cell recycling ratio of 100 %. The results showed that cell recycling had also negative effects on 1,3-PDO fermentation. It was hypothesized that both cell recycling and biomass age caused metabolic shifts to undesired by-products which then inhibited the 1,3-PDO production. On the other hand, the use of hollow-fiber ultrafiltration membrane module was found to be very effective in terms of removal of cells from the fermentation broth.

Continuous production of 1,3-propanediol using raw glycerol with immobilized Clostridium beijerinckii NRRL B-593 in comparison to suspended culture.

The continuous production of 1,3-propanediol (1,3-PDO) was investigated with Clostridium beijerinckii NRRL B-593 using raw glycerol without purification obtained from a biodiesel production process. Ceramic rings and pumice stones were used for cell immobilization in a packed-bed bioreactor. For comparison purpose, a control bioreactor with suspended culture was also run. The effect of hydraulic retention time (HRT) on the production of 1,3-PDO in both immobilized and suspended bioreactors were also investigated. The study revealed that HRT is an important factor for both immobilized and suspended systems and a HRT of 2 h is the best one in terms of volumetric production rate (g 1,3-PDO/L/h). Furthermore, cell immobilization had also obvious benefits especially for the robustness and the reliability of the production. The results indicated that cell immobilization achieved a 2.5-fold higher productivity in comparison to suspended cell system. Based on our results, continuous production of 1,3-PDO with immobilized cells is an efficient method, and raw glycerol can be utilized without any pretreatment.

Optimal conditions for high solid co-digestion of organic fraction of municipal solid wastes in a leach-bed reactor.

Anaerobic co-digestion of organic fraction of municipal solid waste with solid content greater than 20% and chicken manure was investigated using leach-bed reactors in the framework of Middle East and North African countries. The objectives of the experiments were to determine the optimal ratio of organic fraction, chicken manure and solid inoculum, to compare temperature conditions and usage of liquid inoculum or water in percolation process. The highest specific methane yield (SMY) (236 LN ∙ kg-1 VS) was received in the reactors with 20/80 organic fraction/solid inoculum ratio under thermophilic conditions with liquid inoculum percolation. Under the same conditions but mesophilic temperature, SMY dropped by 12%. Replacing liquid inoculum by water led to 172 LN ∙ kg-1 VS. Addition of chicken manure to the substrate mixture positively influences a start-up phase and keeps pH in optimal range 6.5-8, despite the high ammonia concentration.

The effect of corn syrup and whey on the conversion process of CO to ethanol using Clostridium ljungdahlii.

CO is one of the toxic components of syngas, which is the major source of air pollution. Syngas fermentation technology has the ability to convert toxic gases into valuable biofuels, such as ethanol. Fermentative ethanol production is an important method that can be used to promote environmental protection. CO can be converted into ethanol, via the Wood-Ljungdahl pathway, using Clostridium ljungdahlii. The components of the growing medium--especially the trace-element solution and yeast extract--are the main reasons for the high costs associated with this process, however, and this especially impacts scaled-up operations. In this study, cheaper substitutes for these components were used in order to determine their effect on ethanol production. The study comprised three main parts--the optimization of CO concentration, and the substitution of corn syrup and whey powder in the process. The optimum volume of CO for ethanol production was found to be 10 mL. Corn syrup can be used instead of trace-element solution, but the use of yeast extract with the corn syrup was determined to be essential. Up to 1.4 g/L ethanol production was observed with the addition of 15 mL corn syrup. Whey powder had the advantage of being usable without yeast extract, with up to 2.5 g/L ethanol being produced from a 30-g/L concentration. The main finding was that either corn syrup or whey powder can be used as substitutes for expensive basal-medium components.

CO2 utilization via a novel anaerobic bioprocess configuration with simulated gas mixture and real stack gas samples.

CO2, which is considered to be one of the major causes of climate change, has reached to critical levels in the atmosphere due to tremendous consumption of fossil fuels all over the world. In this study, anaerobic bioconversion of CO2 into bio-methane using a novel bioprocess configuration (HYBRID bioreactor) was studied under mesophilic conditions. Varying ratios of H2/CO2 gas mixture and volumetric feeding rates were investigated and no additional organic matter and trace element were needed throughout the study. The maximum methane production of 19 m3 CH4/m3 reactor/d was achieved at a H2/CO2 ratio of 4:1 and feeding rate of 24 m3 gas/m3 reactor/d. It was determined that H2 conversion rate is about 96%. For demonstration purpose, real stack gas sample from a petrochemical industry was also tested under optimized operational conditions. No inhibitory effect from stack gas mixture was observed. This study provided an environmentally friendly and sustainable solution for industries such as petrochemical industry in order to produce extra energy while capturing their waste CO2. Thereby, a sustainable and environmentally friendly model solution was presented for industries with high CO2 emissions.

Sustainable valorization of food wastes into solid fuel by hydrothermal carbonization.

The aim of this study was to comparatively evaluate the effect of hydrothermal carbonization (HTC) conditions on the yield and the fuel properties of hydrochar obtained from food waste (FW) and its digestate (FD). The mass yield of hydrochars from FW and FD were found between 47.0 and 69.8%, 43.0 and 58.2%, respectively, under tested conditions. Based on both mass and energy yields, optimum temperature and duration were selected as 200 °C and 60 min for FW and 200 °C and 30 min for FD. FW and FD hydrochars produced optimum conditions had similar properties to lignite. The selected hydrochars were also subjected to steam gasification and combustion experiments. The combustion reactivity of hydrochars was found to be higher than that of lignite. Steam gasification produced 57-59 mol H2/kg hydrochar. The overall results emphasize the potential of H2 production by integrated systems of dark fermentation, HTC and steam gasification, besides production of solid fuel.

Feasibility of using olive mill effluent (OME) as a wetting agent during the cultivation of oyster mushroom, Pleurotus ostreatus, on wheat straw.

In this study, cultivation of oyster mushroom, Pleurotus ostreatus, on wheat straw substrate containing tap water and olive mill effluent (OME) mixture containing varying volume of OME was studied in order to investigate the feasibility of using OME as an alternative wetting agent and OME's impact on some fundamental food quality characteristics of mushrooms. Time period for mycelial colonization, primordium initiation and first harvest were comparatively evaluated with the control group. It was shown that the use of OME and tap water mixture consisting of OME up to 25% volumetrically was possible for the purpose of commercial mushroom production. Experimental results obtained from substrate containing 25% OME mixture showed no statistically significant difference compared to control group. The negative effects of increasing volume of OME in the mixture were also indicated by bioefficiency, which was found to be 13.8% for substrates wetted with 100% OME, whereas bioefficiency was 53.6% for control group. Increasing volume of OME in the mixture resulted in deformation of fruit body shape, whereas no significant difference in food quality was observed due to the higher amount of OME. This work suggested that the use of OME up to 25% as moisturizer could be considered, especially for the locations having significant number of olive mills and mushroom producers, both as an environmentally friendly solution for the safe and ecological disposal of OME and a practical way for recovering OME's economic value thereby.

Overview of anaerobic treatment: thermophilic and propionate implications.

Difficulties in achieving low propionate concentrations in anaerobically treated effluents are frequently reported in the literature (Ahring, 1994; Kugelman and Guida, 1989; Rimkus et al., 1982), especially at thermophilic temperatures, with concentrations as high as 1000 to 9600 mg/L sometimes produced. This paper will detail the effect of several variables on the performance of both mesophilic and thermophilic regimes. Studies concerning the effect of the following four important factors on performance are included: reactor configuration, inorganic nutrient supplementation, substrate characteristics, and the unique role of microbial consortia proximity in enhancing performance. Reactor configuration modifications, essential nutrient additions, and the importance of close microbial proximity were all found to contribute to improvement in thermophilic anaerobic digestion in all the studies. It was found that, in substrates that shunt significant amounts of the electron donor through propionate, performance was critically related to reactor optimization, with propionate removal efficiency considerably improved using intact upflow anaerobic sludge blanket granules, less so in a homogenized granule slurry blanket, and noticeably reduced even more when the completely stirred reactor configuration of homogenized granules was used. The critical importance of extremely close microbial consortia proximity in maintaining hydrogen intermediates at very low levels to efficiently convert propionate to hydrogen and acetate was demonstrated. Compared to mesophilic digestion, thermophilic digestion manifested elevated levels of propionate, except in the nonmixed reactors, which had close microbial consortia proximity. The reactor configuration with the best results was the anaerobic digestion elutriated phased treatment (ADEPT) scheme, in which the raw sludge was elutriated of its fermenting volatile fatty acids, as they are generated in a short 5- to 8-day solids retention time (SRT) in one reactor and the elutriate then metabolized by passing up through a methanogenic granule or slurry blanket (with its close microbial consortia proximity) in a separate reactor with a 20- to 50-day SRT. Loading rates and performance of the ADEPT reactor configuration were superior to the standard continuously stirred tank reactor, and ADEPT thermophilic temperatures allowed higher organic loading rates without high propionate concentrations in the effluent.

Effect of cell immobilization on the production of 1,3-propanediol.

Immobilized cultures of locally isolated Klebsiella pneumoniae (GenBank no: 27F HM063413) were employed in the continuous production of the high value added biomonomer, 1,3-propanediol from waste glycerol. The effect of hydraulic retention time (HRT) was tested by increasing the dilution rate gradually. Three different immobilization materials (stainless steel wire, glass raschig ring and Vukopor(®)) were tested. The highest productivity was reported with the reactor filled with stainless steel wire as 4.8 g/(L hours) and the highest 1,3-propanediol concentration was 17.9 g/L when glass raschig rings were used as the packing material with the HRTs of 0.5 hours and 1.5 hours, respectively. Compared to the suspended culture system 1,3-propanediol production was more resistant to shorter hydraulic retention times that leads to higher 1,3-PDO productivities. All three of the materials are good candidates for immobilization purpose; however, stainless steel wire and Vukopor(®) are better support materials in terms of productivities. The results reported in this study revealed that continuous fermentation in a packed-bed bioreactor system is a suitable method to enhance 1,3-propanediol production.

Comparative evaluation of pumice stone as an alternative immobilization material for 1,3-propanediol production from waste glycerol by immobilized Klebsiella pneumoniae.

In this study, pumice stone (PS), which is a vastly available material in Turkey, was evaluated as an alternative immobilization material in comparison to other commercially available immobilization materials such as glass beads and polyurethane foam. All immobilized bioreactors resulted in much better 1,3-propanediol production from waste glycerol in comparison to the suspended cell culture bioreactor. It was also demonstrated that the locally available PS material is as good as the commercially available immobilization material. The maximum volumetric productivity (8.5 g L(-1) h(-1)) was obtained by the PS material, which is 220 % higher than the suspended cell system. Furthermore, the immobilized bioreactor system was much more robust against cell washout even at very low hydraulic retention time values.

1,3-Propanediol production potential of Clostridium saccharobutylicum NRRL B-643.

Owing to the significant interest in biofuel production in the form of biodiesel, vast amount of glycerol as a waste product is produced all over the world. Among the economically viable and ecologically acceptable solutions for the safe disposal of this waste, biotechnological conversion of glycerol into a valuable bioplastic raw material, namely 1,3-propanediol (1,3-PDO) seems to be very promising. In this study, 1,3-PDO production potential of Clostridium saccharobutylicum NRRL B-643 was studied and the results were compared with other types of anaerobic microorganisms (Clostridium spp., Pantoea agglomerans, Ochrobactrum anthropi, Chyreseomonas luteola, and Klebsiella pneumoniae) and aerobic microorganisms (Lactobacillus spp.). The results were important for understanding the significance of C. saccharobutylicum NRRL B-643 among other well-known 1,3-PDO producer species. According to the screening results only C. saccharobutylicum (B-643) was able to consume feed glycerol almost entirely. However, 1,3-PDO production yield was found to be 0.36mol/mol which is lower than that of Clostiridium beijerinckii (B-593). B-593 showed the highest value of production yields with 0.54 mol/mol. This microorganism is seen as a promising type for further 1,3-PDO studies, because it has the highest substrate utilization percentage among others. In this regard, this microorganism may have an important role in tolerating and converting glycerol during fermentation into 1,3-PDO.

Evaluation of two wild types of Pleurotus ostreatus (MCC07 and MCC20) isolated from nature for their ability to decolorize Benazol Black ZN textile dye in comparison to some commercial types of white rot fungi: Pleurotus ostreatus, Pleurotus djamor, and Pleurotus citrinopileatus.

Biological decolorization of Benazol Black ZN, a reactive azo-type textile dyestuff, was comparatively studied using 3 different commercial-type white rot fungi strains (Pleurotus ostreatus, Pleurotus cornucopiae var. citrinopileatus, Pleurotus djamor, and 2 wild types of P. ostreatus (MCC07 and MCC20) isolated from the nature. The initial dye concentrations in the medium were 500 and 1000 mg.L-1. All the organisms studied decolorized Benazol Black ZN to varying degrees. At low dye concentration, both commercial and wild type of P. ostreatus resulted in the best decolorization, conversely, wild-type P. ostreatus (MCC07) was found to be much more robust against increasing dye concentration and provided the best decolorization efficiency at high dye concentration.

Coastal zone problems and environmental strategies to be implemented at Edremit Bay, Turkey.

This case study examines the coastal zone problems focusing on the existing conflicts between tourism and commercial activities on the coasts of Edremit Bay, Turkey, and attempts to suggest solutions to these problems. Edremit Bay is a characteristic example of such a conflict in collective use of natural resources. The study area, with its 100-km-long sandy beach, naturally attracts different coastal user groups with different beneficial expectations: in terms of rest and recreation for one group and commercial gain offered in a variety of ways for another group. Significant coastal zone problems exist in the study area. Deterioration of shoreline due to tourism activities and illegal constructions, damage to the coastal ecosystem due to domestic/industrial wastewater discharges and some agricultural activities, and disordered urbanization are only a few of the many problems. The data presented here were partly derived from field study and partly collected from local state or private organizations. In this study, it is emphasized that there is a need for viable economic and environmental strategies to be designated in Edremit Bay, Turkey, in order to provide sustainable resource use. For this purpose, an integrated project together with a relevant planning chart including subprojects is also suggested. The success of a local environmental protection management project depends on active participation of all stakeholders including governmental organizations and nongovernmental organizations.