Ultrasonic Disintegration of Animal Manures before Anaerobic Digestion

Ultrasonic disintegration increases methane (CH₄) yield, decreases solid retention time (SRT) and improves the overall performance of anaerobic digestion. This is the result of the disintegration of biosolids and bacterial cells in animal manures and the release of intracellular components due to the solubilization of the particulate matter. Hielscher ultrasonic reactors for the pretreatment of animal manures lead to more methane (biogas) and more soluble chemical oxygen demand (SCOD) in anaerobic digestion.

Anaerobic Digestion of Animal Manures

Animal wastes are anaerobically digested to reduce organic matter content, for odor reduction and to reduce greenhouse gas emissions from covered systems. Another potential benefit is the reduction of manure pathogens. Typical animal wastes for digestion are swine manure (pig manure, hog manure), dairy manure or beef feedlot manure, chicken manure, turkey manure, pit scrape, liquid manure, feedlot runoff and manure effluent.

Ultrasonic Disintegration

Ultrasonic cavitation disintegrates organic solids and increases the quantity of dissolved organic substrate as well as the degradation rate and the digestibility of biosolids during the anaerobic digestion process. This pretreatment makes more surface available for the subsequent anaerobic digestion. The result is an improved conversion of biosolid particles to biogas. This enhances the biodegradability, increases the biogas yield and increases the soluble chemical oxygen demand (SCOD).

Ultrasonic Reactors

Hielscher supplies ultrasonic disintegrators for the in-line pretreatment of small and large volume throughput. All ultrasonic reactors are designed to run continuously (24hrs/7d/365d) for maximum equipment utilization. Depending on factors, such as the waste composition, TS or solid retention time in the digester, the required equipment capacity varies between 2 and 10 kW per 1 m³/hour for most installations. Hielscher ultrasonic probes and reactor geometries are optimized based on many years of practical experience in the pretreatment of waste and sludge before digestion. This is important, as the configuration of sonication parameters and hydraulic design has a significant impact on the disintegration effect. Hielscher ultrasonic reactors allow for the processing of more viscous (less diluted) material for higher process efficiency. Also, Hielscher ultrasonic devices feature an outstanding electrical efficiency greater than 81% – resulting in a higher disintegration performance. The use of a macerator before sonication reduces larger particles and fibers and improves uniformity of the input into the ultrasonic system.

Co-Digestion of Waste Mixtures

The benefits of ultrasonic disintegration before digestion extend beyond animal manure. Ultrasonication improves the hydrolysis of co-digestion of manures with food waste, municipal sewage sludge or even crude glycerin from biodiesel production. Ultrasonic disintegration as a pretreatment before for mesophilic or thermophilic co-digestion shows significantly higher volumetric methane yields, lower H₂S (odor) and lower effluent ammonia than non-sonicated material. Small amounts of glycerin (4 to 6%) added to manure before ultrasonic disintegration lead to a significant increase in biogas production.

Benefits of Ultrasonication

An obvious effect of ultrasonic disintegration is the increase in biogas yield. However, even greater savings result from lower trucking costs and lower dewatering costs due to the reduction of waste after material digestion. Shorter retention times improve the digester capacity and may help to avoid the installation of an additional digester. Less odor due to lower H₂S and less effluent ammonia are of environmental significance.

Installation and Retrofitting

Hielscher ultrasonic reactors can easily be integrated in new projects or retrofitted to existing anaerobic digesters. You can test the effects for your waste material in small scale, e.g. using a UIP2000 (20kHz, 2000 watts) system with cascatrode probe and flow cell reactor. The modular design of high capacity ultrasonic systems (e.g. 10x UIP4000, 40 kilowatts) allows for the flexible installation and gradual upgrade. In particular when retrofitting existing digesters, the costs for the sonication equipment are quickly amortized by the cost savings and biogas revenues. Please contact us for free information!

Biogas – Renewable Energy

Biogas is a environmentally friendly, renewable energy. While biodiesel and bioethanol are mostly produced from food or non-food crops, biogas from manure uses a farming waste product. Biogas does not require energy-intense distillation or aggressive chemicals and has very small carbon footprint. Ultrasonically assisted anaerobic digestion produces clean, green and renewable energy for many livestock operations at a cost competitive with or below commercial natural gas prices.