Food waste composting

The objective of this thesis was to increase our knowledge of issues relevant to process problems in large-scale composting. The investigations focused on acid-related process inhibition and the relationships between temperature, aeration, evaporation and the scale of the process. Three manuscripts are summarised in the thesis proper. The first investigated composting at different scales; at full-scale, in a 2 m high reactor and in a one-litre vessel. The process in the reactor resembled the full-scale process, but the theoretical calculations showed that the heat losses from the reactor were large. About 0.45 m of glass wool would be necessary to produce similar thermal properties in the reactor as in the full scale plant. Accumulation of acids was studied in the second investigation. Different amounts of active compost were used as a starting culture in rotating three-litre reactors, which were fed daily with fresh waste and water. In reactors with a large amount of starting culture, more than four times the daily feed, a well-functioning process with high temperature, high CO2 production and high pH was established. In reactors with a starting culture less than twice the daily feed, the composting process failed. The temperature was below 42 °C and the CO2 production was small. In these reactors the pH was low and organic acids accumulated. It was concluded that acid inhibition of fed-batch processes can be avoided if sufficient amounts of a good starting culture are used. In the third investigation, the combined effects of temperature and pH on the degradation were studied. Small samples of compost from the initial acidic phase were treated with sodium hydroxide to raise the pH. This resulted in high respiratory activity in samples at all pH levels at 36 °C and in those with pH over 6.5 at 46 °C. However, at 46 °C the activity was very low in samples with pH below 6.0. This shows that a combination of high temperature and low pH can inhibit the composting process. The influence of the composting temperature on the evaporation was also analysed. Simulations showed that the difference in evaporation at different temperatures was very small for the same degradation, although there were large variations in airflow. Finally, addition of water to compost is discussed. It is often necessary to add water when composting energy-rich substrates, since otherwise the process may be halted due to drying before the compost has stabilised

Wastewater disposal to landfill-sites: a synergistic solution for centralized management of olive mill wastewater and enhanced production of landfill gas

The present paper focuses on a largely unexplored field of landfill-site valorization in combination with the construction and operation of a centralized olive mill wastewater (OMW) treatment facility. The latter consists of a wastewater storage lagoon, a compact anaerobic digester operated all year round and a landfill-based final disposal system. Key elements for process design, such as wastewater pretreatment, application method and rate, and the potential effects on leachate quantity and quality, are discussed based on a comprehensive literature review. Furthermore, a case-study for eight (8) olive mill enterprises generating 8700 m(3) of wastewater per year, was conceptually designed in order to calculate the capital and operational costs of the facility (transportation, storage, treatment, final disposal). The proposed facility was found to be economically self-sufficient, as long as the transportation costs of the OMW were maintained at <= 4.0 (sic)/m(3). Despite that EU Landfill Directive prohibits wastewater disposal to landfills, controlled application, based on appropriately designed pre-treatment system and specific loading rates, may provide improved landfill stabilization and a sustainable (environmentally and economically) solution for effluents generated by numerous small- and medium-size olive mill enterprises dispersed in the Mediterranean region

Dry anaerobic digestion of organic residues on-farm - a feasibility study

Objectives The feasibility study shall answer the following questions: Are there economical and ecological advantages of on-farm dry digestion biogas plants? How the construction and operation parameters of a dry digestion biogas plant influence environment, profit, and sustainability of on-farm biogas production? The aim of the feasibility study is to provide facts and figures for decision makers in Finland to support the development of the economically and environmentally most promising biogas technology on-farm. The results may encourage on-farm biogas plant manufacturers to develop and market dry anaerobic digestion technology as a complementary technology. This technology may be a competitive alternative for farms using a dry manure chain or even for stockless farms. Results Up to now farm scale dry digestion technology does not offer competitive advantages in biogas production compared to slurry based technology as far as only energy production is concerned. However, the results give an over-view of existing technical solutions of farm-scale dry digestion plants. The results also show that the ideal technical solution is not invented yet. This may be a challenge for farmers and entrepreneurs interested in planning and developing future dry digestion biogas plants on-farm. Development of new dry digestion prototype plants requires appropriate compensation for environmental benefits like closed energy and nutrient circles to improve the economy of biogas production. The prototype in Järna meets the objectives of the project since beside energy a new compost product from the solid fraction was generated. On the other hand the two-phase process consumes much energy and the investment costs are high (>2000 € m-3 reactor volume). Dry digestion on-farm offers the following advantages: Good process stability and reliability, no problems like foam or sedimentation, cheap modules for batch reactors, less reactor capacity, reduced transport costs due to reduced mass transfer in respect of the produced biogas quantity per mass unit, compost of solid digestion residues suitable as fertiliser also outside the farm gate, use of on-farm available technology for filling and discharging the reactor, less process energy for heating because of reduced reactor size, no process energy for stirring, reduced odour emissions, reduced nutrient run off during storage and distribution of residues because there is no liquid mass transfer, suitable for farms using deep litter systems. These advantages are compensated by following constraints: Up to 50% of digestion residues are needed as inoculation material (cattle manure does not need inoculation) requiring more reactor capacity and mixing facilities. Retention time of dry digestion is up to three times longer compared to wet digestion requiring more reactor capacity and more process energy, filling and discharging batch reactors is time and energy consuming. We conclude that only farm specific conditions may be in favour for dry digestion technology. Generally, four factors decide about the economy of biogas production on-farm: Income from waste disposal services, compensation for reduction of greenhouse gas emission, compensation for energy production and - most important for sustainable agriculture - nutrient recycling benefits. Evaluation of the results We did not find any refereed scientific paper that includes a documentation of an on-farm dry digestion biogas plant. It seems that we tried first. We also could not find any results about the biogas potential of oat husks, so we may have found these results first. Farm scale production of anaerobically treated solid manure for composting is new. Dry fermentation biogas plants offer the possibility to design solid manure compost by variation of fermentation process parameters. From different scientific publication databases we found about 10 000 references concerning biogas research during the past 10 years. Less than ten are dealing with biogas reactors for non-liquid substrates on-farm. Recent research mainly concentrates on basic research, biogas process research for communal waste, large-scale biogas plants, and research on laboratory level. This mirrors the fact, that production of research papers is rather financed than product development on site. Our conclusion is that it seems worldwide to be very difficult or even impossible to find financial support for on site research, especially for on-farm prototype biogas reactors. We suppose the following reasons for this fact: biogas plant research requires proficiency in many different scientific disciplines, lack of co-operation between engineering and life sciences, high development costs to transfer basic research results into practical technical solutions, low interest of researchers because on site and on-farm research enjoys low appreciation in terms of scientific credits, portability of farm specific design and process solutions is difficult. Our conclusion is that on site and on-farm research has to be supported by funding agencies if integration of biogas and bio energy into the farm organism is considered as an important target within the agricultural policy framework. Future research on both dry fermentation technique and biogas yield of solid organic residues may close present knowledge gaps. Prototype research may offer competitive alternatives to wet fermentation for farms using a solid manure chain and/or energy crops for biogas production. To encourage farmers and entrepreneurs to foster the development of dry fermentation technology support in terms of education and advisory services is also necessary

Integrating dark and light biohydrogen production strategies: towards the hydrogen economy

Biological methods of hydrogen production are preferable to chemical methods because of the possibility to use sunlight, CO2 and organic wastes as substrates for environmentally benign conversions, under moderate conditions. By combining different microorganisms with different capabilities, the individual strengths of each may be exploited and their weaknesses overcome. Mechanisms of bio-hydrogen production are described and strategies for their integration are discussed. Dual systems can be\ud divided broadly into wholly light-driven systems (with microalgae/cyanobacteria as the 1st stage) and partially light-driven systems (with a dark, fermentative initial reaction). Review and evaluation of published data suggests that the latter type of system holds greater promise for industrial application. This is because the calculated land area required for a wholly light-driven dual system would be too large for either centralised (macro-) or decentralised(micro-) energy generation. The potential contribution to the hydrogen economy of partially light-driven dual systems is overviewed alongside that of other biofuels such as bio-methane and bio-ethanol

A technical and economic evaluation of selected biomass-to-fuels conversion processes

Thesis (M.S.)--University of Oklahoma.The major objective of this study was to determine the economic and technical feasibility of existing methods for producing readily useable fuel from biomass. A thorough literature search was undertaken in an effort to evaluate the most promising and advanced biomass conversion processes about which published information was available. A ranking method was then developed to compare the selected processes. A major problem that was encountered was the lack of completeness in the reported data. This incompleteness indicated that there was a major need for essential design information concerning changes of biomass during storage and detailed process design and scale-up information, which simply were not available. The most promising processes were found to be gasification and bioconversion types. The pyrolytic oil processes were less feasible by this ranking method

Pilot-scale Study on Anaerobic Digestion Applied to a Saline Industrial Waste Activated Sludge

In the field of municipal wastewater treatment, anaerobic digestion is a well-established, effective process for stabilization of organic sludge with the attractive features of low operating costs and production of methane as a useful by-product. Application of anaerobic digestion for the treatment of saline industrial wastewater sludge, however, has not been well established. The studies described in this thesis were conducted with the overall goal of assessing the feasibility of mesophilic anaerobic digestion processes for treatment of waste activated sludge (WAS) containing moderate salinity (approximately 3% m/v). Experiments employed two 30-gallon conical-bottom HDPE reactors. In the first phase of testing, intended to produce acclimated microbial populations, both reactors were operated in batch mode without mixing for a period lasting 48 days. In the second phase of testing, two different reactor operating strategies were evaluated. One reactor was unmixed with operation at a 60-day target hydraulic residence time, while the second was a mixed system with a 30-day target hydraulic residence time. Temperature, pH, alkalinity, solids concentrations, organic acid concentrations, biogas evolution rates, and biogas methane content were measured over a period lasting more than 180 days. Results demonstrate that elevated salinity of 3% m/v does not preclude effective anaerobic digestion. Both reactors exhibited stable pH, alkalinity, and gas composition with \u3e60% methane. The high VSS destruction efficiency, 41.3% (HR reactor) and 49% (LR reactor), showed the reactor well functioned. Both reactors exhibited a methane content of approximately 65% after 70 days (July 9, 2008) operation, which indicates that the lipid degradation was not inhibited under this digestion condition

Reducing organic loading of anaerobic lagoons with high-rate anaerobic digestion : reactor performance and economic analysis

This research examined the potential of reducing dairy waste lagoon organic loading with high-rate anaerobic digestion (HRAD) systems operating at hydraulic retention times (HRT) of less than one day. An in-line approach was examined as a means of pre-treating the wastestream to reduce the lagoon organic load. An off-line approach was examined as a means to reduce the organic load within the anaerobic lagoon through the removal of volatile fatty acids. Two types of HRADs were tested, an anaerobic sequencing batch reactor (ASBR) and a downflow anaerobic filter (DFAF), both of which operated at 25 and 35° C. Initial plans were to use the HRADs for removal of organics by operating upstream of anaerobic lagoons. However, initial results of this approach were unsatisfactory, and it was suspected that the reactors were removing organic materials through settling rather than biodegradation. This possibility was tested by performing a chemical oxygen demand (COD) mass balance to determine if suspended solids settling was the main method of wastewater treatment. The mass balance demonstrated that 100% of the COD removed in the ASBRs, and 72% of the COD removed in the DFAFs, could be attributed to settling instead of biodegradation. The second experiment demonstrated that volatile fatty acids (VFA), mainly acetic (HAc), could be removed from the anaerobic lagoon if an HRAD was used in an off-line mode. Off-line operation would involve pulling HRAD influent from below the lagoon surface with the effluent being returned to the lagoon. At low loading rates (1.0 and 3.0 kg HAc m-3 d-1), both reactor types had treatment efficiencies greater than 30%. At the lowest loading there was no difference among the reactor types at the same temperature (P \u3e 0.33 for both temperatures). At the higher loading, there was a difference across reactor types at the same temperature (P \u3c 0.0001 for both temperatures). At a loading of 6.0 kg HAc -3 d-1 the ASBRs proved to be ineffective; whereas, the DFAJFs had removal efficiencies \u3e 70% for both temperatures. The DFAFs also provided \u3e 40% removal of HAc at loading rates of 24 kg HAc -3 d-1; thereby, suggesting that DFAFs are superior to ASBRs for removing accumulated VFAs at high loading rates. The high removal rates at the low HRTs allow for a smaller volumetric reactor and thereby a more feasible system. An economic model was developed to explore the feasibility of installing a DFAF system compared to expanding an existing anaerobic lagoon. The model computed the equivalent annualized annuity (EAA) of the two alternatives with a DFAF reactor operating at 0.8 kg HAc -3 d-1 and 2.4 kg HAc -3 d-1. The model was run for herd sizes ranging from 100 to 800 cows and overloads ranging from 10 to 100%. The results of the model suggests that for facilities with small herd sizes (\u3c 400 cows) and overloads less than 70%, expanding the lagoon is the preferred alternative. With large herd sizes (\u3e 400 cows) and overloads greater than 70%, the DFAF was suggested to be the preferred alternative

EVALUATION OF MULTIPLE FEEDSTOCKS FOR CODIGESTION

In the U.S., a move toward the use of anaerobic digestion (AD) technologies for solid waste management has been slow. However, recently, a number of factors have coalesced to renew interest in AD because of its potential to produce renewable energy from the wastes. It is well known among AD practitioners that every waste material is unique, and each must be evaluated on a case-by-case basis for a particular digester project. A review of existing literature revealed that the guidance provided by it was not of a quality that would promote and assist with rapid U.S. AD development and advances. The aim of this research was to address some of these deficits and provide some new information to inform feedstock testing reliability and reproducibility. A database of codigestion articles published between 2000 and 2014 was compiled to examine the nature and quality of existing literature and also new researchers to filter research articles based on a variety of criteria that include feedstocks, operational parameters, and the types of information reported. The database is expandable and available for hosting on a website. Database analysis revealed that 32% of the authors measured biogas production but not methane (CH4) output specifically. Only 27% of the studies used food to microorganism (F:M) ratio as an operational parameter, and 8% reported both F:M and the nutrients expressed as carbon-to-nitrogen (C:N) ratio. The batch codigestion experiments revealed that even in the absence of acclimated sludge or alkalinity supplementation, poultry litter (PL) and DAF in equal weight percent loadings proved to be stable cosubstrates. Further, mixes in ratios of PL60:FW15 (poultry litter: food waste) with the remainder brown grease (BG) or DAF were also successful despite the fact that FW and DAF failed in the biochemical methane potential (BMP) and anaerobic toxicity assays (ATA) tests due to acidification. The BG was only mildly inhibitory in ATA testing and performed well in the BMP test with alkalinity supplementation. All batch, BMP and ATA experiments showed glycerin (GLY) and/or canola seed hull cake inhibited CH4 production. Although acidification was implicated in the canola ATA, it was not the cause of failure in the BMP test or in either GLY test; propionate accumulation or toxins may have been responsible. Methane yields in the BMP tests showed BG to be the most productive (371±76 mL CH4/gVS), and paper, PL, and cattle manure (CM) had yields in the 120–150 mL CH4/gVS range. PL and CM were stimulatory in the ATAs, with all other feedstocks showing varying degrees of inhibition. This finding is interesting in light of the fact that feedstock cell counts showed that PL (as well as CM and DAF) contain more live cells per gram volatile solids than the seed used as inoculum. The semi-continuous reactors demonstrated that a mix with up to eight feedstocks could be managed in a stable digestion; however, mixes with lipid-laden feedstocks, high organic loading rates or short solids retention time led to foaming and fouling of two of the reactors. DAF exposed to thermal pretreatment produced 170±22 mL CH4/gVS, while untreated DAF yielded no CH4. Similarly pretreated CM showed a two-fold increase in CH4 yield, but the same was not true for sewage sludge, where pretreatment inhibited CH4 production. Thermal pretreatment of PL had no effect on CH4 production, but, along with CM and DAF, it had a positive net energy balance. The energy analysis based on pretreatment studies reported in the literature revealed that chemical and biological pretreatment were the only methods that reliably yielded a net energy gain. Mechanical, thermal, and thermochemical pretreatment were less successful at yielding net positive energy values. Taken together, this body of work offers a roadmap for codigestion research. Ready access to recent literature is provided along with guidance about the important procedural, operational and reporting features required for sound study. A reproducible batch protocol is described that includes attention to nutrient and inoculant balance, to gas collection and analysis, and to the use of controls. If replicated, it will allow for better comparisons among laboratories. The importance of replication of semi-continuous or continuous flow studies is highlighted, due to the inherent variability between reactors. A discussion of the relevance and application of the BMP and ATA tests is offered, and data from some novel feedstocks is reported. Feedstock cell counts suggest that F:M ratios for some substrates need to be adjusted to account for live cells entering with the feed

Particle size and metal distributions in anaerobically digested pig slurry

Particle size distribution and trace element patterns were studied in a full-scale anaerobic digestion plant treating pig slurry. Mass balance was established for major (N, P, K, Ca, Fe, Mg and S) and minor (Al, Cu, Mn and Zn) elements. Most of the elements were conserved through the process but part of the P, Ca, Mg and Mn was deposited as crystals lining the digester. In the dry matter of the slurry, Cu and Zn occurred at between 170 and 2600 mg kg1 due to pig diet supplements. Analyses of particle size distributions in raw and digested slurries showed a general shift in distribution towards larger sizes due to degradation of small and easily degradable particles as well as formation of large microbial filaments. Graded sieving of digested slurry showed metals to be mainly present on 3–25 lm particles. Less than 2% Cu and Zn was removed by passage through a 250 lm rotary screen

Design of Auto Mix Single Stage Anaerobic Digester and Aspen Plus Simulation for Biogas Production

Bio fuels have been considered to be the viable alternatives and the supportive sources for the depleting fossil fuels under the objective of satisfying the energy demand. The work explored the possibility of biogas production in various operational scales. The present work can be categorized into two parts. In the first part, the work has surveyed various digester designs under operation and focused on the mixing and intermittent aeration that are not under light in the regular practice. The digester gas collector configuration that could promote the mixing and intermittent aeration was designed. The setup was run on 20 L scale with an objective of observing the gas production phenomenon. The recommended operational solutions were modified and implemented in the form of a 50 L digester setup to observe the performance improvements in attaining self-buffering capacity and sensitivity to the acidic feed stocks. Further suggested modifications lead to the final design that could promote intermittent aeration and mix the digester constituents without the use of impeller and with minimal or no power consumption depending on the amount of gas produced. An advanced design called compartmental digester design was next presented for the medium to large scale applications which was run on 200 L scale in a semi continuous mode using cow dung as substrate and was tested for the feasibility. The second part of our work focused on simulation of a two stage anaerobic digester configuration for studying the kinetics of hydrolysis, acidogenesis and acetogenesis and methanogenesis in three different reactors. In this study, kitchen waste stream were analysed for biogas production which was compared with the results of NISARGRUNA biogas plant (BARC) for the validation of the model and the model with same kinetics was then used to analyse the gas production from poultry manur