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FAQs About HotRot Systems

How does HotRot differ from other systems?

HotRot is a continuous, flow-through, in-vessel composting system. It incorporates a horizontal composting chamber that has a shaft running longitudinally through it. This shaft has tines, or arms, attached and rotates periodically and slowly. The shaft redistributes moisture and heat and aids aeration ensuring the composting process operates at high efficiency. See our document – HotRot a new generation composting system.pdf.

Are odours generated?

The composting process and mature compost do not generate significant odours. However, odours can be associated with the raw waste and may therefore be emitted by the untreated waste. Global Composting Solutions Ltd offers a contractual OdourFree Guarantee – see OdourFree Guarantee contract version.pdf, we also offer guidelines for compost storage and utilisation – Guidelines for compost storage and utilisation.pdf

What does the OdourFree Guarantee mean?

Simply put, if the system is designed and installed by Global Composting Solutions and operated according to our instructions, we will guarantee no objectionable odours past the site boundary – see OdourFree Guarantee short version.pdf.

How can HotRot offer an OdourFree Guarantee?

The odour or contaminant levels in air emitted from composting systems are a function of the efficiency of the process. The more efficient a system is the lower the initial odour and contaminant level. The HotRot system is also fully enclosed and its efficiency means that a relatively compact biofilter can be used to treat the air discharged from the system.

Why do HotRot units not produce leachate?

Excess water is released as vapour and discharged via the exhaust air. It does not accumulate and "leach" from the system. See our document – HotRot units do not produce leachate.pdf.

What is the residence time in a HotRot unit?

There are two parts to this answer. First it must be recognised that the HotRot unit is a continuous system, waste enters the unit periodically throughout the day and compost is also discharged at the same time. There is no need to completely empty a unit. It generally takes 10-12 days for a particle of waste to pass from the front of the vessel until it is discharged as compost from the other end.

How long does it take?

This is the same as residence time – 10-12 days inside the vessel.

How can you produce stable compost in 10-12 days?

This again relates to the efficiency of the HotRot process. Most composting systems can be considered to idle along; HotRot is the system running down the highway. See our documents – Part 3 - understanding HotRot.pdf and Why is HotRot different.pdf.

Do I need to cure or mature the compost?

We generally recommend that all compost be stored in static open piles for 2-4 weeks. Compost can be spread on agricultural land with little or no storage. If material is going to be bagged it should also be dry with moisture content less than 30%. Curing or storage allows ammoniacal-nitrogen generated during the composting process, and present in the product, to be converted to nitrate-nitrogen. This biological process can only occur when the material cools to less than 30oC but occurs rapidly once the material is applied to soil.

 

How much compost is produced?

This varies but a rule of thumb is for every 1.0 tonne in you will get between 0.5 to 0.7 tonne of compost out.

How much waste can a HotRot unit process?

HotRot units are manufactured in three sizes. The smallest HotRot 1206 has a throughput capacity of 0.2-0.4 and is designed for smaller on-site applications. The largest unit, the HotRot 3518, with a throughput of 10-15 tonne per day is designed for multi-unit installations for municipalities and larger waste management companies. The intermediate sized HotRot 1811 has a throughput capacity of 1.8-2.5 tonne per day when supplied with an integrated feed hopper or 1.0-1.8 tonne per day when supply with a less efficient bin-lifter feed unit. The 1811 can either be used singularly or in pairs as an on-site solution or used in multi-unit installations for smaller municipalities and local waste management contracts.

Where is the system made?

The HotRot units are manufactured in China under the strict supervision of an ex-pat Kiwi. The concrete for the hull of a HotRot 3518 will be cast locally. We have a network of sub-contractors in New Zealand and worldwide that supply ancillary equipment such as shredders, feed hoppers, conveyors and screens, etc.

Isn't shipping the units globally expensive?

No, equipment is large and generally fills an entire shipping container. Containers are efficient to handle and transport. Ocean-freight is cheap and the cost of transport from a port to a client's site is generally less than it would be to truck from a factory. Total freight costs are generally only 2-3% of the value of a contract.

How is waste introduced into the HotRot unit?

HotRot units are generally supplied with a feed hopper and integrated conveyor. The feed hopper is able to take up to 2 days' processing capacity. The conveyor is linked to, and the feed regulated by, the HotRot unit's control system. Alternatively, we can also supply bin-lifters for the smaller units that allow direct feeding of 120- or 240-litre wheelie bins (trash carts).

Can you supply shredders and other equipment?

Yes. Global Composting has preferential supplier status with manufacturers of some shredders. We also supply feed hoppers, conveyors (belt and screw), products screens and dewatering equipment. These are manufactured for us by partner companies who we have established long-term relationships and who understand the difficulties many of the waste we deal with present. Global Composting works with its customers to identify their needs and provide an integrated solution from waste reception, through pre-processing, composting and final product handling and use.

Do you provide operator training?

Yes, operator training is generally provided as part of the installation and commissioning process. We can also provide additional training and refresher courses as needed.

What spare parts do I need?

There is very little that can go wrong with a HotRot unit. Motors are standard off the shelf units and available from many local suppliers. We generally supply an initial stock of lubricants – oil and grease – and some key parts. Spares for ancillary equipment, especially shredders, are discussed with each client at time of supply.

Do I need to enclose my HotRot units in a building?

No, the HotRot units themselves are completely weatherproof and do not require a building. However, a building may be required to control odours generated by storing and/or shredding/macerating raw waste prior to composting. Buildings may also be required in extreme climates. HotRot units can operate outside in temperature between -5oC (-25oC with a "winterisation" package) and +40oC. The electrical and control system can operate between 0oC and +45oC.

Do I need planning permission or consents?

You will need to check the requirements of your local council or regulatory authority. In general it would be normal to require consent or a permit to install the equipment and one to operate the plant.

Is temperature measured and recorded?

Each unit incorporates multiple temperature probes along the length of the vessel. Temperatures are continually monitored and logged by the control system. We offer options for remote access and data download.

What wastes can I process?

The HotRot process can handle virtually any organic waste. The main parameters to regulate are moisture content and porosity; optimally moisture should be around 50-60%. However, particle size, the nutrient balance and pH of the material also influence compost quality. HotRot units can easily cope with contaminants such as plastic bags, cans and even glass; many of these materials can then be removed from the compost by screening. HotRot is designed for highly putrescible wastes and works best with food, animal and sewage wastes.

Do I need to add wood?

Yes, woody material is added to improve porosity (bulk) and reduce the overall moisture content of the waste. Ground or shredded wood or tree prunings are ideal as they both reduce the overall moisture and provide structure (bulk/porosity). Timber can be sourced from packing cases and pallets used to transport goods and equipment to site as well as timber dunnage. Leaf and yard waste (garden waste) can also be used but seasonal variation in both availability and moisture need to be considered. Woody material must be processed to meet the specifications detailed in our document - Amendments and bulkers.pdf and HotRot – generic specifications for use.pdf.

Can I use paper and cardboard instead of wood?

Not entirely, while cardboard can be used to "dry" food and other wet wastes it is not ideal as a bulking agent as cardboard tends to compact when wet, resulting in a mass of material that is difficult to aerate. Additionally, a high proportion of cardboard and paper would dramatically increase the carbon to nitrogen ratio, thus retarding the composting process; paper and cardboard should ideally make up less than 10% of the mass of material being composted.

Is there an optimal particle size for woody material used in the HotRot process?

Yes, for hard woody materials, no larger than 75 mm on the longest axis, ideally 10–50 mm. By spending effort on reducing the particle size at the start of the process, the compost process can proceed faster and the need to screen compost at the end of the process can be avoided.

Do I need to shred food waste?

No, food waste does not need shredding. Even whole chicken mortalities can be placed inside the HotRot unit without shredding.

Do I need to shred other waste?

This depends on the type and volume of waste to be processed. Leaves, weeds, grass clippings and other small vegetation can be composted without prior processing. Branches will need chipping to reduce their size. Animal carcasses should be cut up into fist-sized pieces or smaller. Kitchen and restaurant wastes and offal may be composted without prior shredding or macerating.

Do I need to screen my compost?

If the material entering the process is small (i.e., well shredded wood has been used) then screening may not be required. However, if larger particles are composted or the material is contaminated with plastic etc, then screening will be required. Screening can often allow the recovery of some bulking material for reuse.

What are the running costs of a HotRot unit?

Power consumption ranges from approximately 20 kWh per tonne of waste through to approximately 35 kWh per tonne, depending on the material being processed and other equipment being used (i.e., shredders).

What labour input is required?

A small HotRot unit may require an operator for about 1 hour per day. Larger plant will generally use 50-75% less labour than a corresponding sized plant using other technology.

What maintenance do I need to do?

There are grease nipples on each machine that need periodic greasing. The gearbox oil should also be replaced at least every 12 months. It is recommended that the tines and bearings be visually inspected annually. HotRot and its agents offer preventative maintenance and support contracts, however, generally maintenance can be performed by any competent operator.

What safety features are incorporated into the design of the HotRot unit?

Each tine can take a large proportion of the full torque load of the motor. The motor is also torque load controlled and systems to prevent overload are implemented. The feed system is enclosed, which prevents unauthorised entry into the system. The outlet is shrouded to prevent access. Emergency stops are located at convenient points on the HotRot machine, ancillary equipment and control panel.