Background and Purpose.

This project is based upon a high pressure manure separator that was developed and built in former projects. One of the results from these projects was that the high pressure piston separator could be used as a refuse separator by changing the operation parameters.

The purpose of this project is to investigate the separation efficiency of the existing hydraulic piston at operation parameters relevant for commercial operation of piston waste separators.

The objective formulated in the original application sent to the Danish Environmental Protection Agency states:

The waste separation process should result in a maximum of 25 % reject(weight percent), while the separated biomass delivered to the anaerobic digestion should not contain more than 0,1 % contaminants.

In this project the following technical parameters have been investigated listed in the order, they are considered important for the optimisation of the separator.

	Separation efficiency
	Plastic separation efficiency
	Capacity
	Wear on the separator
	Energy consumption
	Chemical characterisation of the products.

Technical results

In this project 4 separation chambers have been built and tested:3 chambers with slots, 1 mm, 0,6 mm and 0,25 mm; and, one chamber with holes.

Furthermore a low pressure screw separator has been designed and built in order to remove the potentially remaining plastic in the biomass.

	With a separation chamber with slots, 8-30 % of reject has been obtained with refuse from AFAV and 7 % reject with refuse from R-98.
	With the separation chamber with holes 22-45 % reject has been obtained on AFAV refuse and 20-33 % reject on R98 refuse.

These reject percentages are obtained with separation piston pressures from 200-450 bar.

The energy consumption for a piston separation process is approx. 10-20 kWh pr. ton refuse.

The lifetime for a separation chamber with slots is expected to be 100-500 hours.

The lifetime for an optimised hole chamber is expected to be over 1000 hours.

A one stage piston separator can deliver 80-90 % of the total biogas potential in the incoming refuse into the biomass fraction.

	On AFAV refuse 0,2-1 % plastic in the biomass has been obtained on separation chambers with slots and 0,1 % on the chamber with holes.
	On R 98 refuse 0,1-0,3 % plastic has been obtained.

These plastic concentrations have been derived from refuse of highly variable composition and quality.

The hole chamber will remove 70-85 % of the thin plastic bags. All other types of plastic are completely removed.

The chemical analyses from DTU of potential environmentally damaging fractions and emissions show levels adequately below all thresholds and thus in accordance with current legislation. However, the visible amount of plastic (of about 0,1-0,3 %) appears not to be acceptable to the end-users, the farmers. Subsequently, a two- step unitincluding a screw separator has been constructed and tested in order to remove all visible plastic from the biomass treated in the high pressure piston unit.

An optimised second stage separator will be able to deliver 80-90 % of the biogas potential in the biomass fraction from the piston separator. Thus 70-80 % of the total biogas potential of the initial refuse can be found in biomass treated in the two stage process. This fraction contains no or very little plastic.

The energy consumption of a 2 stage separator will be approx. 15-30 kWh pr. ton of refuse.

Conclusion

Based on the trials on the fourth chamber and the two-step separation process the results are in accordance with the targets set for total reject percentage and the quality of the biomass for anaerobic digestion. However, for AFAV refuse it will be necessary to eliminate garden refuse and diapers which today are included in the refuse fraction separated.

The trials on the different chambers have shown that the original slot chamber must be altered due to durability problems. Trials made on a chamber with drilled holes have demonstrated satisfactory durability of this chamber.

The potential for up-scaling the plant is believed to be minimally 10.000 tons waste/year/unit.

Reject percentage and plastic content in the biomass, both controlled by the separation pressure, are approximately reverse proportional.

All plastic qualities except the very thin qualities used for refuse collection are completely removed.

The chemical analyses from DTU of potential environmentally damaging fractions and emissions show levels adequately below all thresholds and thus in accordance with current legislation. However, the visible amount of plastic (of about 0,1-0,3 %) appears not to be acceptable to the end-users, the farmers.

A one stage piston separator can deliver 80-90 % of the total biogas potential in the incoming refuse into the biomass fraction. Compared to test results from other separators in Denmark this is a very competitive result.

Refuse fractions such as diapers and garden refuse all end up as reject, thus it is recommended that refuse for high pressure separation not contain these fractions.

Refuse collected in biodegradable paper or plastic bags will, even if low plastic threshold values are required, enable use of a one-stage separation technique. If traditional thin plastic bags are used, and visible plastic is a concern, a 2-stage process will normally be required.