Material AND Energy Recovery at its best, the Example of AVA Augsburg, Germany

The waste management companies of the city of Augsburg, the district of Augsburg and the district of Aichach-Friedberg, Germany, are active around the clock for the approx. 1.2 million inhabitants in their disposal area. With the initial operation of a biowaste fermentation plant in 2013 and 2016, AVA has become one of Germany's largest players also in the field of material recycling. The reciprocal supplementation and interaction of the plant components result in extremely positive synergies.

Key Data of AVA

On an area of 235,000 m², AVA disposes of over 350,000 tons of waste per year. The waste consists of the residual waste from households, commercial and hospital waste, as well as approx. 90,000 tons of biowaste per year.

The two core elements of the AVA are the waste-to-energy plant and the biowaste fermentation plant, which, in ideal interaction, enable the recycling of organic and thermal waste from the catchment area that cannot be used for other purposes. The plants are operated all year round, around the clock.

Parallel to this, AVA also takes over the tasks: treatment of hospital waste, slag processing, mobile heat transport, power generation through photovoltaics, and much more.

  

Using the existing plant conglomerate, AVA generates process steam, district heating, electrical energy, compost, biogas/biomethane and liquid fertilizer and thereby actively reduces the production of greenhouse gases. This is because the greenhouse gases methane (CH4) and nitrous oxide (N2O), which are harmful to the climate and are produced during fermentation, cannot be significantly reduced by the biofilters normally used.

Another important part of this climate-relevant component of AVA's recycling facilities is the recovery of scrap metals from the slag.

AVA Production Figures 2018

    

 

The Biowaste Fermentation Plant

 

The installed technique is ideal for the fermentation of organic residues. The residues are collected separately in the organic waste bin. They include grass, leaves and green waste as well as food leftovers and other organic fractions from the kitchen.

 

Delivery hall / Preparation

  

          Large-scale treatment

• Mechanical pre-treatment with a shredder (90% biowaste + 10% structural material)
• Throughput capacity up to 50 t/h
• Separation of the fractions > 60 mm and < 60 mm with separation of impurities using a star screen
• Sorting out the FE metals in the < 60 mm fraction via magnetic separator

Intermediate storage

• 4 intermediate storage tanks of 200 m³ each
  => continuous feeding for 2.5 days without delivery (weekends, public holidays, etc.)

• Material feed via overhead screw conveyors

• Material discharge via milling drums and scraper chain conveyors (in intermediate storage) and screw conveyors

Fermenter

3 plug-flow fermenters with a total of 4.800m³ useful volume One mixer per fermenter for substrate mixing and substrate heating Anaerobic thermophilic Process at > 50 °C Substrate input TS approx. 30% Substrate discharge TS approx. 23-25% Top-mounted double membrane gas storage tank with approx. 1,500 m³

 

Dewatering (pressing)

1 screw press + 1 vibrating screen per fermenter Liquid digestate: TS approx. 17 - 20 vol.% Solid fermentation residue: DM approx. 40 vol.% Degree of rotting III-IV

Additional decanter for separation of solids from the press water. Decanted centrate TS approx. 7 - 10 vol.%

The fermentation residue remaining at the end of the fermentation process is dewatered in screw presses, subjected to post-rotting in a separate warehouse and processed into valuable compost before it can be passed on to interested customers. The compost and the liquid fermentation product are subject to constant RAL quality assurance by the German Federal Compost Association (Bundesgütegemeinschaft Kompost).

Biogas Treatment Plant

The biogas obtained during the fermentation process is then processed into biomethane and used for further energy production.

-Treatment of the biogas using membrane technology (up to up to 700 m3/h bio natural gas) -No methane emissions No methane slip Post-treatment of the exhaust air flow is not required

 

Pre-treatment  

Max. Output 1,150 Nm³/h Biogas Max. output 700 Nm³/h Biomethane Pre-pressure blower for adjusting the pressure upstream of the scrubber and activated carbon container (approx. 150 mbar) Scrubber for tempering the biogas and separating ammonia

3 activated carbon lines with 2 activated carbon containers each (approx. 870 kg activated carbon per container)  For the separation of hydrogen sulphide (H2S) and terpenes  With iron-2-chloride dosing into the fermenters, an H2S concentration in the biogas of approx. 50 - 100 ppm is achieved

 Gas Separation

3 biogas compressors for compressing the biogas to 9 - 11.5 bar(g)

Post-treatment of lean gas stream

   

• 2 CO2 compressors for compressing the CO2 gas flow to approx. 17 bar(g)

• Regenerative activated carbon filter for cleaning the of the CO2
  

• Refrigeration system for cooling and liquefying the CO2 (approx. -25 °C)

• CO2 stripper to separate the gaseous CH4 from the liquid CO2

Further advantages from the proximity to the waste-to-energy plant

- Incineration of wastewater or the liquid fermentation product in the AHK

• Waste water is mainly recirculated.
• Wastewater from the biofilter area, the biogas upgrading plant and the condensates from the rotting hall are fed to the AHKW for incineration.
• The liquid fermentation product produced is primarily used in agriculture.
• Alternatively, it can be incinerated in the household waste furnace lines.

 

 

Conclusions

The local proximity to the waste-to-energy plant and the technical interaction of individual process steps generate ideal synergies. For example, waste water that accumulates and is no longer required in the further process, as well as sorted out impurities (e.g. plastic foils) can be fed directly to the waste-to-energy plant for incineration.

Likewise, no costly and time-consuming after-treatment of exhaust air streams is necessary. Exhaust air streams from the area of the presses, the settling and storage basins, as well as the intensive rotting, can be fed to the waste-to-energy plant where they can be co-incinerated. As these are loaded with ammonia and contain traces of methane, this significantly reduces greenhouse gases and potential odors after the biofilter. The existing biofilter is thus relieved. 

In return, the biowaste fermentation plant can be supplied with electricity and, if necessary, with heat (to heat the fermenters) by the waste-to-energy plant. In this way, the biogas produced can be completely converted into biomethane and used as a complementary and storable form of energy to PV and wind power.

Both plants share various resources:

• Scale
• Traffic area
• Personnel (electricians, locksmiths ...)
• Company officers (immission control, waste, fire protection, ...)
• 24h occupied control room in waste-to-energy plant
• Supply/disposal systems (electricity, water, wastewater, etc.)

This ideally reduces both energy requirements and operating costs.