Ann C. Wilkie

STILLAGE CHARACTERIZATION AND ANAEROBIC TREATMENT OF ETHANOL STILLAGE FROM CONVENTIONAL AND CELLULOSIC FEEDSTOCKS

Abstract A technical evaluation of stillage characterization, treatment, and by-product recovery in the ethanol industry was performed through a review of the scientific literature, with particular emphasis on solutions pertinent to a cellulosic-based ethanol production system. This effort has generated substantial information supporting the viability of anaerobic digestion for stillage treatment followed by land application on biomass crops for nutrient recovery. Generally, the characteristics of stillage from cellulosic materials appear comparable to those of conventional sugar- and starch-based feedstocks. However, the data on cellulosic stillage characteristics and treatment parameters are extremely limited and highly variable. This has significant impacts on the capital costs and biogas recovery of anaerobic treatment systems predicted from these data. In addition, technical questions remain unanswered with regard to stillage toxicity from untested feedstocks and the impact of heavy metal leaching when acid hydrolysis reactors are fabricated from corrosion-resistant alloys. Thermophilic anaerobic digestion of ethanol stillage achieves similar treatment efficiencies and methane yields compared to mesophilic treatment, but at almost twice the organic loading rate. Therefore, application of thermophilic anaerobic digestion would improve process economics, since smaller digesters and less stillage cooling are required. Downstream processes for stillage utilization and by-product recovery considered worthy of continued investigation include the production of feed (from single cell protein and/or algae production), color removal, and production of calcium magnesium acetate. This study finds that sustainable and economically viable solutions are available for mitigating the environmental impacts which result from large-scale biomass-to-ethanol conversion facilities. However, further research in some areas is needed to facilitate successful implementation of appropriate technology options.

Recovery of dairy manure nutrients by benthic freshwater algae

Harnessing solar energy to grow algal biomass on wastewater nutrients could provide a holistic solution to nutrient management problems on dairy farms. The production of algae from a portion of manure nutrients to replace high-protein feed supplements which are often imported (along with considerable nutrients) onto the farm could potentially link consumption and supply of on-farm nutrients. The objective of this research was to assess the ability of benthic freshwater algae to recover nutrients from dairy manure and to evaluate nutrient uptake rates and dry matter/crude protein yields in comparison to a conventional cropping system. Benthic algae growth chambers were operated in semi-batch mode by continuously recycling wastewater and adding manure inputs daily. Using total nitrogen (TN) loading rates of 0.64-1.03 g m(-2) d(-1), the dried algal yields were 5.3-5.5 g m(-2) d(-1). The dried algae contained 1.5-2.1% P and 4.9-7.1% N. At a TN loading rate of 1.03 g m(-2) d(-1), algal biomass contained 7.1% N compared to only 4.9% N at a TN loading rate of 0.64 g m(-2) d(-1). In the best case, algal biomass had a crude protein content of 44%, compared to a typical corn silage protein content of 7%. At a dry matter yield of 5.5 g m(-2) d(-1), this is equivalent to an annual N uptake rate of 1,430 kg ha(-1) yr(-1). Compared to a conventional corn/rye rotation, such benthic algae production rates would require 26% of the land area requirements for equivalent N uptake rates and 23% of the land area requirements on a P uptake basis. Combining conventional cropping systems with an algal treatment system could facilitate more efficient crop production and farm nutrient management, allowing dairy operations to be environmentally sustainable on fewer acres.

Growth of benthic freshwater algae on dairy manures

A potential alternative to land application of livestock manures for cropproduction is the production of algae to recover the nitrogen andphosphorus present in the manure. Compared to terrestrial plants,filamentous algae have exceedingly high growth and nutrient uptake rates. Moreover, they are capable of year-round growth in temperate climates,can be harvested on adapted farm-scale equipment, and yield a biomassthat should be valuable as an animal feed supplement. The objective of thisresearch was to evaluate algal turf scrubber (ATS) technology to removenitrogen, phosphorus and chemical oxygen demand from raw andanaerobically digested dairy manure. Laboratory-scale ATS units wereoperated by continuously recycling wastewater and adding manure effluentsdaily. ATS units were seeded with algal consortia from a nearby streamand grown using dairy manures from two different dairy farms. Algalbiomass was harvested weekly and dried prior to analysis for total Kjeldahlnitrogen, total phosphorus, and inorganic constituents. Wastewater sampleswere analyzed for total Kjeldahl nitrogen, ammonium, nitrate,orthophosphate, conductivity and chemical oxygen demand. Using atypical manure input containing 0.6–0.96 g total nitrogen day-1,the dried algal yield was approximately 5 g m-2 day-1. Thedried algae contained approximately 1.5–2% phosphorus and 5–7%nitrogen. Algal nitrogen and phosphorus accounted for 42–100% ofinput ammonium-nitrogen (33–42% of total nitrogen) and 58–100%of input total phosphorus, respectively.

PRODUCTION AND NUTRIENT REMOVAL BY PERIPHYTON GROWN UNDER DIFFERENT LOADING RATES OF ANAEROBICALLY DIGESTED FLUSHED DAIRY MANURE1

Growing algae to scrub nutrients from manure presents an alternative to the current practice of land application and provides utilizable algal biomass as an end product. The objective of this study was to assess algal growth, nutrient removal, and nitrification using higher light intensities and manure loading rates than in the previous experiments. Algal turfs, with periphyton mainly composed of green algal species, were grown under two light regimes (270 and 390 μmol photons·m−2· s−1) and anaerobically digested flushed dairy manure wastewater (ADFDMW) loading rates ranging from 0.8 to 3.7 g total N and 0.12 to 0.58 g total P·m−2·d−1. Filamentous cyanobacteria (Oscillatoria spp.) and diatoms (Navicula, Nitzschia, and Cyclotella sp.) partially replaced the filamentous green algae at relatively high ADFDMW loading rates and more prominently under low incident light. Mean algal production increased with loading rate and irradiance from 7.6±2.71 to 19.1±2.73 g dry weight· m−2·d−1. The N and P content of algal biomass generally increased with loading rate and ranged from 2.9%–7.3% and 0.5%–1.3% (by weight), respectively. Carbon content remained relatively constant at all loading rates (42%–47%). The maximum removal rates of N and P per unit algal biomass were 70 and 13 mg·g−1 dry weight·m−2·d−1, respectively. Recovery of nutrients in harvested algal biomass accounted for about 31%–52% for N and 30%–59% for P. Recovery of P appeared to be uncoupled with N at higher loading rates, suggesting that algal potential for accumulation of P may have already been saturated. It appears that higher irradiance level enhancing algal growth was the overriding factor in controlling nitrification in the algal turf scrubber units.

Enhancement of anaerobic methanogenesis from napiergrass by addition of micronutrients

Mesophilic anaerobic digestion of Napiergrass (Pennisetum purpureum Schum.), supplemented with nitrogen and phosphorous, resulted in a low rate of methane production and high volatile fatty acid (VFA) concentrations. Daily addition of micronutrients — nickel, cobalt, molybdenum, selenium and sulfate (as a sulfur source) — increased methane production by approximately 40% and significantly decreased the VFA concentrations.

Cyanobacterial process for renovating dairy wastewater

Abstract Dairy operations in Florida face the dual problem of water pollution and air pollution (odors) as a result of the large amounts of manure produced on the farms. Ground and surface waters are contaminated by nitrogen present in seepage and runoff. A low-cost method of treatment of dairy wastewater is to convert the dissolved nutrients to microalgae biomass in engineered ponds designed to maximize photosynthetic production through solar energy. Laboratory experiments conducted on effluent from an anaerobic lagoon of a modern dairy showed that cyanobacteria (= blue-green algae) grow well on dairy wastewater and that nitrogen removal is rapid and complete. Ammonia nitrogen concentrations were reduced from 100 mg l −1 to less than 1 mg l −1 in seven days. Maximum removal rate was 24 mg l −1 per day. Prospects for nitrogen recycling are considered.

Ecology and microbiology of biogasification

Abstract The biodegradation of organic matter to form methane and carbon dioxide requires the interactions of diverse populations of bacteria. The roles of each of these organisms in the process and how they interact with each other is understood only in a rudimentary way. This paper describes the investigation of the microbial ecology of the anaerobic degradation of biomass feedstocks.

Methanogenesis from Propionate in Sludge and Enrichment Systems

The biological formation of methane from organic matter is a complex microbiological process involving many physiologically dependent relationships between and among a diversity of heterotrophic fermentative and methanogenic bacteria. The methanogenic metabolism of all organic matter leads to the formation of the same types of intermediates namely H2, C02, and formate, acetic, propionic, and butyric acids. These compounds are, in turn, converted directly or indirectly to methane by methanogenic bacteria alone or acting together with non-methanogenic heterotrophs. These latter organisms may be syntrophic partners of the methanogens or simply members of a broader food-chain. Estimates on the sum:total of the fermentative contributions by these few metabolic intermediates account for 100% of the methane formed in a typical digestor. The importance of acetate as a direct methanogenic intermediate is already well established (5,6). Evidence points to a more complicated role played by the metabolism of butyrate and propionate in this fermentation. The main focus of the present paper is to examine the role of propionate in methanogenesis not only to re-assess its importance as a source of methane or methanogenic precursors in digestors but also to examine the biochemical and physiological basis for its conversion to methane.

Aquatic plants: an opportunity feedstock in the age of bioenergy

There is a growing impetus to identify and develop bioenergy feedstocks that can be harnessed in ways that do not require major land-use intensification or use of food crops. Although invasive aquatic plants have long been regarded as an intriguing potential feedstock because of their high growth rate in natural water bodies, most contemporary management is based on plant control rather than utilization. This review presents a comparative life cycle overview of modern aquatic plant control and alternative bioenergy utilization programs, highlighting costs and benefits associated with both approaches. Given recent advances in harvester and bioenergy conversion technologies, it may be cost effective to incorporate utilization techniques in many water bodies, particularly if ancillary benefits associated with nutrient removal and greenhouse-gas reductions are given monetary credit. Pilot projects and site-specific evaluations are, however, needed to determine the ultimate scale in which bioenergy production from aquatic plants will be feasible.

Life cycle assessment of nutrient remediation and bioenergy production potential from the harvest of hydrilla (Hydrilla verticillata)

Hydrilla (Hydrilla verticillata) is one of the worlds most problematic invasive aquatic plants. Although management of hydrilla overgrowth has often been based on use of chemical herbicides, issues such as the emergence of herbicide-resistant hydrilla biotypes and the need for in situ nutrient remediation strategies have together raised interest in the use of harvester machines as an alternative management approach. Using a life cycle assessment (LCA) approach, we calculated a range of net energy and economic benefits associated with hydrilla harvests and the utilization of biomass for biogas and compost production. Base case scenarios that used moderate data assumptions showed net energy benefit ratios (NEBRs) of 1.54 for biogas production and 1.32 for compost production pathways. NEBRs for these respective pathways rose to 2.11 and 2.68 when labor was excluded as a fossil fuel input. Base case biogas and compost production scenarios respectively showed a monetary benefit cost ratio (BCR) of 1.79 and 1.83. Moreover, very high NEBRs (3.94 for biogas; 6.37 for compost) and BCRs (>11 for both biogas and compost) were found for optimistic scenarios in which waterways were assumed to have high hydrilla biomass density, high nutrient content in biomass, and high priority for nutrient remediation. Energy and economic returns were largely decoupled, with biogas and fertilizer providing the bulk of output energy, while nutrient remediation and herbicide avoidance dominated the economic output calculations. Based on these results, we conclude that hydrilla harvest is likely a suitable and cost-effective management program for many nutrient-impaired waters. Additional research is needed to determine how hydrilla harvesting programs may be most effectively implemented in conjunction with fish and wildlife enhancement objectives.