How long does the in-vessel stage take?
- Retention or residence time depends on the level of stability required and its phasing with sanitization while in-vessel.
- ABPR set mandatory sanitization time/temperature requirements together with maximum particle sizes; as those sanitization regimes (at 60 C for 2 days or 70C for 1 hour) also kill the great majority of the bacteria, fungi and actinomycetes that do the composting, it is uneconomic to retain the bio-matter in-vessel after the sanitization.
- By stabilizing before sanitizing as the Alpheco systems do, a higher level of stability is achieved in a shorter time than vice-versa and thereby retention time is minimized.
- The EU is expected to legislate someday on the level of stability at which composted biowastes cease to be controlled so may be traded as a product, albeit still immature. Once a load has crossed that threshold, it may be removed from the waste-licensed site and tipped out to mature on some cheaper site such as the headland of the field where it is to be spread.
What civil engineering infrastructure is needed?
- Aergestors, their aeration valves and the Aerator-cum-Biofilter of each group are best on a concrete slab 9m wide with guide rails for the Aergestors' RoRo rollers.
- A sub-surface drain running along the front edge to site sump tank can collect condensate, any leachate and harvest rainwater; a sump-pump can then recycle that water to increase moisture in new loads or inside any Aergestor as required.
- The reception building and main access roadway should also be concrete but the rest of the site on which RoRo trucks manoeuvre can be cheap hardcore.
- A 3-phase supply is required to each Aerator and a computer LAN from each Aerator to a site office is best in a sub-surface conduit.
How big is the building?
- ABPR require a building for biowaste reception, particle size reduction and mixing. As the header photograph illustrates, if the waste collection regime uses conventional refuse trucks, the building needs to be big and high enough to accept them.
- If big bio-bins are issued for 'green' wastes, the few large bits of wood they attract usually mean the whole load must be shredded, which leads to a big building possibly with dust extraction and some sound-proofing.
- If however, the householders are restricted to catering and only soft, green wastes, perhaps by having smaller bins like the brown one hanging on the left of the big, blue recyclables bin, the red residuals bin could also be small providedthe bio-bin is emptied weekly simple maceration rather than shredding will be OK and the building can be much smaller.
- For six years of R&D, Alpheco deployed 120-litre bins to several supermarkets and collected them on a simple flatbed truck from which they were tipped directly in to the mixer and thence loaded in to an Aergestor thus eliminating double handling and avoiding daily cleaning of mess on the floor.
What do the Alpheco systems cost?
- Capital costs are so dependent on the throughput and retention time that they must be estimated for particular circumstances.
- The economical use of concrete and the 'plug and play' design of the systems, which saves lengthy on-site installation costs, keep capital costs well down.
- Enquirers should also state feedstocks and if they want the particle sizing, mixing and loading equipment estimated too.
- Operating costs will usually be highly competitive even with windrowing(!) due to energy efficiency, labour saving from avoiding mechanical shovels etc. plus the 'fill & forget' computerized control and temperature recording.
- Site cleanliness by design also saves significant labour.
- Lease funding can also be offered in contrast for fixed installations due to the demountable design and the long life expectancy. The latter is partly due to the stainless steel bodies etc and also from keeping the relatively costly Aeration system static while the Aergestors are out on the road.
What are the USPs?
- Flexibility: due to modular design.
- Heat recovery: Although the heat energy is unsuitable for electricity generation, it may be more valuable than the compost!
- Energy efficiency: Sharing the variable speed blower between many Aergestors coupled with the reversible (upward or downward) aeration flows use far less power than agitated systems or the frequent turning of windrows. These are the core of Alpheco's patent.