Pretreatment For Anaerobic Digestion Research Articles

An economic assessment of algal turf scrubber technology for treatment of dairy manure effluent

Controlling the input of nitrogen (N) and phosphorus (P) from dairies and other livestock operations into the surrounding air- and water-sheds poses both technical and economic challenges to the agricultural community. The purpose of this paper is to assess the economics of algal turf scrubber treatment technology at the farm-scale for a hypothetical 1000-cow dairy. Costs were developed for farms with and without anaerobic pretreatment. The majority of capital costs were due to land preparation, installation of liner material, and engineering fees. The majority of operational costs were due to energy requirements for biomass drying, pumping water, and repayment of capital investment. On farms using anaerobic pretreatment, waste heat from burning of biogas could be used to offset the energy requirements of biomass drying. In addition, biogas combustion exhaust gas could then be recycled back to the algal system to supply dissolved inorganic carbon for optimal algal production and pH control. Under the best case (algal system coupled with anaerobic digestion pretreatment), the yearly operational costs per cow, per kg N, per kg P, and per kg of dried biomass were $454, $6.20, $31.10, and $0.70, respectively. Without anaerobic digestion pretreatment, the yearly operational costs were 36% higher, amounting to $631 per cow, $8.70 per kg N, $43.20 per kg P, and $0.97 per kg of dried biomass. For perspective, a recent survey of 36 Maryland dairy farms found long-term annual profits of about $500 per cow. As no market currently exists for manure grown algal biomass, our cost analysis does not include any value of the biomass generated during manure treatment. In addition, there are a variety of potential uses for the algal biomass from manure treatment that could defray treatment costs. Future opportunities for dairies to participate in nutrient trading approaches to watershed nutrient management may also become important.

Solubilization of organic sludge by thermophilic aerobic bacteria as a pretreatment for anaerobic digestion

Solubilization of organic sludge by thermophilic aerobic bacteria as a pretreatment for anaerobic digestion was investigated. The thermophilic bacteria which solubilized organic sludge were isolated from the thermophilic aerobic digestion reactor. The bacterium type SPT2-1 could grow at pH ranging from 5.0 to 8.5 with optimal temperature at 60-70 degrees C. In batch experiments, 25-30% of volatile suspended solids (VSS) in the pre-heated sludge were solubilized on inoculating with the isolated bacteria although little was solubilized without inoculation. The isolated bacteria appeared to secret the extracellular enzymes including proteases and amylases. In continuous flow experiments, sludge solubilization rate (VSS removal) was around 40% under aerobic as well as microaerobic conditions. No accumulation of volatile fatty acids in the treated sludge was observed under aerobic conditions while significant amounts of them were accumulated under microaerobic conditions. Production of biogas on anaerobic digestion of the microaerobically-pretreated sludge was increased by 1.5 when compared with the sludge without pretreatment.

The Application of Ultrasound as a Pre-Treatment for Anaerobic Digestion

The sonication of sewage sludge can be used as a pre-treatment to anaerobic digestion. The anaerobic digestion process has the potential to become more efficient through the break-up and solubilisation of solid sludge particles. Here, the performance of anaerobic digestion was compared when fed with unsonicated sludge and sludges sonicated at two different intensities. The tests were run as a series of batch flasks and three 100 litre anaerobic digesters. The data from the batch tests clearly indicated the positive effect on anaerobic digestion through gas production (increase by 15%) and volatile fatty acid production. The data from the anaerobic digesters was less distinct. Little difference was observed between the volumes of gas produced, however there was an increase in methane production, volatile solids reduction and the soluble COD by up to 6%, 5.5% and 15% respectively when a comparison was made between sonicated and unsonicated sludges. However, sonication was observed to have a detrimental effect on the sludge dewaterability. This effect was more acute when a higher sonication intensity was used, however anaerobic digestion did reduce this effect. Therefore, while sonication can enhance anaerobic digestion, the negative effect on the sludge properties must be considered before applying this technique to any site where dewatering processes are used. The two different sonication intensities indicated that there was a minimal difference in performance. Therefore, the application of low intensity sonication can allow both process and economic benefits.

Treatment of liquid fraction separated from liquidized food waste in an upflow anaerobic sludge blanket reactor

Thermochemical liquidization as a pretreatment for anaerobic digestion of food waste was studied using a laboratory-scale upflow anaerobic sludge blanket (UASB) reactor for a period of 82 d. Model food waste (approximately 90 wt% moisture content) was thermochemically liquidized at 175°C for 1 h. The liquidized food waste was separated into a solid phase (6–10 wt%) and a liquid phase (85–89 wt%). The diluted liquid phase was continuously treated by anaerobic digestion using a UASB reactor at 35°C. The volumetric loading rate was increased stepwise to 6.4–7.2 g total organic carbon (TOC)/ l-reactor/d. Methane production was found to be approximately 0.35–0.61 l/g-TOC removed. The range of TOC removal efficiencies was 67–69% at an influent TOC concentration of 10.1–11.1 g/ l and a volumetric loading rate of 4.8–5.3 g-TOC/ l-reactor/d. This treatment process using an UASB reactor could be suitable for resource recovery from food waste.

Application of ceramic membrane as a pretreatment in anaerobic digestion of alcohol-distillery wastes

Pretreatment of alcohol-distillery wastes with ceramic membranes was performed prior to anaerobic digestion. Ceramic membranes with 0.05 μm pore size were chosen based on the particle size distribution in raw wastes. In this pretreatment, chemical oxygen demand (COD) was reduced from 36,000 to 18,000 mg/l and suspended solids were almost completely removed. The permeates from the ceramic membrane were further separated by ultrafiltration, but further COD reduction by using the PM30 and PM10 membranes was not achieved. Mixed stillages exhibited higher fouling tendency than pure naked barley stillage. Several cleaning methods were attempted to recover water flux. Although lumen flushing was effective, hydrogen peroxide proved to be the most effective cleaning agent. The negative flux recovery after nitric acid cleaning could be explained by the ligand exchange theory. The performance of digester was greatly improved with membrane pretreatment, specially in the ease of naked barley based stillage.