WO2009081124A2

WO2009081124A2 - Disposal of water-containing waste

Info

Publication number: WO2009081124A2
Application number: PCT/GB2008/004203
Authority: WO
Inventors: Susan Elizabeth Clarke
Original assignee: Morgan Everett Limited
Priority date: 2007-12-22
Filing date: 2008-12-19
Publication date: 2009-07-02
Also published as: GB0725172D0; WO2009081124A3; GB201010217D0; GB2468444A

Abstract

Methods are provided for processing sanitary waste comprising the step of chemical treatment of the waste to release liquid present therein prior to further treatment of the waste. Also provided is the use of a chemical agent to facilitate and/or enable release of liquid from sanitary waste prior to further processing. Methods of improving the efficiency of sanitary waste processing comprising chemical treatment of the sanitary waste to release absorbed liquid prior to further processing are also provided.

Description

DISPOSAL OF WATER-CONTAINING WASTE

The present invention relates to the processing or treatment of sanitary waste from a range of sources.

Municipal waste disposal is a growing problem, with the majority of this waste being buried in landfill sites. Suitable locations for landfill sites are relatively uncommon due to the strict hydro-geological requirements, avoidance of water table contamination and other environmental considerations. In short, there is an increasing scarcity of suitable waste burial sites and an urgent need for alternative methods of waste disposal.

Known methods of waste disposal include incineration and waste pyrolysis. However, the efficiency of incineration and pyrolysis processes are adversely affected by the presence of water or other liquid components in the waste. In general, it is necessary to remove most or substantially all of the liquid component of the waste before incineration or pyrolysis can be completed.

The significance of the presence of liquids in waste can be seen, for example, in the PyroPure® method of disposal of waste (described in International patent application no. PCT/GB2007/00853). This method takes untreated waste into a sealed chamber and thermally destroys it. The initial stage involves heating the waste to around 500⁰C and the wetter the waste the longer this stage takes as the waste has to be dried before the temperature can reach its correct level. It is this stage that consumes the most power and therefore the economies of the process depend very much on the efficiency of this stage.

It has been determined that, in certain waste streams, on average the wettest waste is used nappy and incontinence pad waste. A single incontinence pad can contain up to 1 litre of liquid, which means that a full load of such waste can contain several litres of liquid which has to be dried, e.g. before the thermal destruction process can start.

The majority of nappies and incontinence pads contain a gel composed of what is generally known as a "Super Slurper" polymer. These polymers were developed by ARS chemists William M. Doane, George F. Fanta, Edward B. Bagley, and Mary Ollidene Weaver, now retired, in the 1970s, and are described in US 3,997,484 and US 3,981 ,100. In essence, the technology involves grafting a natural polymer in cornstarch to a synthetic one made from petroleum. The scientific name - saponified starch-graft polyacrylonitrile copolymers - was deemed too cumbersome for informal use so the name "Super Slurper" was coined. Today totally synthetic polymers have been developed based on similar principles.

There are now a number of different "Super Slurpers" but all are essentially hydrophilic non-toxic crosslinked polymers that can absorb 400-800 times their weight in water, but cannot dissolve because of their three-dimensional polymeric network structure. The polymers are extremely strong and the absorbed water is effectively trapped or locked in by the polymer. It is not possible to remove the trapped water by physical methods such as the use of pressure or physical destruction of the polymer-containing items. For example, shredding or squeezing does not eliminate any of the absorbed liquid and even placing a saturated nappy in a vice will not produce liquid.

The nappy and incontinence pad materials, the polymer and the contents of the nappies and incontinence pads can all be destroyed by thermal processing methods including incineration and pyrolysis, e.g. using the PyroPure® method, but the presence of absorbed liquid significantly impairs the efficiency of such processes. At present the only way of removing the absorbed liquid content is by evaporation. However, the energy input to remove the liquid content in this way is considerable and does not accord well with the desire to reduce energy usage, e.g. in view of environmental concerns. The process would be significantly more power and time efficient if at least some of the liquid could be eliminated before the start of the process.

Accordingly, it is an object of the present invention to provide methods for waste treatment, especially the treatment of sanitary waste, that release the liquid from the waste before the further processing steps are carried out. A further object of the invention is to provide more efficient methods of waste processing. It is desirable that such methods should be simple and use readily available, inexpensive materials.

Accordingly, a first aspect of the invention provides a method for processing sanitary waste comprising the step of chemical treatment of the waste to release liquid present therein prior to further treatment of the waste.

A second, related, aspect of the invention provides use of a chemical agent to facilitate and/or enable release of liquid from sanitary waste prior to further processing.

A third aspect of the invention provides a method of improving the efficiency of sanitary waste processing comprising chemical treatment of the sanitary waste to release absorbed liquid prior to further processing.

A fourth aspect of the invention provides an apparatus for treating sanitary waste to release absorbed liquid prior to further processing comprising a first chamber, wherein the first chamber is adapted to receive sanitary waste and a chemical agent, wherein exposure of the sanitary waste to the agent facilitates and/or enables release of absorbed liquid.

In more detail, a first aspect of the invention provides a method for processing sanitary waste comprising the step of chemical treatment of the waste to release liquid present therein prior to further treatment of the waste. The method is particularly suited to the processing and destruction of waste comprising nappies, incontinence pads and/or other absorbent sanitary items, either as part of mixed general waste, e.g. domestic waste, or in waste that substantially consists of sanitary waste, e.g. segregated waste from hospitals, nurseries and residential care homes.

In the context of the present invention, it will be appreciated that the term sanitary waste is intended to include any type of waste that includes sanitary items, which may be present in various proportions of the total waste. In some embodiments, the sanitary waste comprises a high proportion of sanitary items or consists entirely of sanitary items. In other embodiments, the sanitary waste may comprise a high proportion of non-sanitary items, e.g. general waste items, in addition to sanitary items. The term sanitary waste includes waste of the type known as "inco" and/or "sanpro", either alone or in combination with other waste types.

The sanitary items present in the sanitary waste may be any items which in use absorb one or more bodily fluids or excreta including, but not limited to, nappies, incontinence pads, sanitary towels, tampons, sick bags and the like. Typically, the sanitary waste will include at least some items which, in use, absorb liquids that can subsequently be released as free liquid by carrying out the methods of the invention.

It will be appreciated that the liquid released from the sanitary waste treated according to the invention will typically consist primarily of water but may also include other substances in solution or suspension. In many cases the liquid will be an aqueous solution of biological origin such as urine. However, in all cases the improved efficiency provided by the methods of the invention results from avoiding the need to remove the liquid component of the sanitary waste by evaporation of water vapour. In light of this, the liquid component of the sanitary waste is sometimes referred to herein as water, and the terms water and liquid are generally used interchangeably herein.

It is envisaged that the sanitary waste will comprise one or more absorbent polymeric materials, typically one or more hydrophilic non-toxic crosslinked polymers, e.g. polymeric materials comprising one or more cornstarch-derived polymeric components or synthetic analogues thereof. In many instances the sanitary waste will comprise a significant proportion of items comprising "Super

Slurper" polymers and the methods of the invention are particularly suited to the processing of such sanitary waste, in which the absorbent polymeric materials comprise one or more saponified starch-graft polyacetonitrile copolymers.

Without wishing to be bound by any particular theory, "Super Slurper" polymers are widely believed to operate as follows:

In the dry powdered state the chains of the polymer are coiled and lined with carboxyl groups, i.e. (-COOH) groups. When hydrated with water, the carboxyl groups dissociate into negatively charged carboxylate ions (-COO^"1). These ions repel one another along the polymer chain thereby widening the polymer coils and allowing water to move into contact with more carboxyl groups. As the polymer continues to uncoil, it ultimately swells to form a gel-like consistency. The polymer does not form a solution because it still has crosslinking due to hydrogen bonding where hydrogen atoms in water molecules positioned between the polymer chains are attracted to the oxygen atoms in the carboxylate ions lining the chains. Hence the absorbed water is retained within the expanded polymer structure.

The present applicant has recognised that if this retained water could be released prior to processing and disposal of the waste without relying on evaporation there would be significant advantages, not least in terms of reduced time and energy expenditure in waste processing. According to the invention, this can be achieved by chemical treatment of the waste to break down the polymer.

Thus, in a preferred embodiment of the invention, the sanitary waste is treated with an agent that breaks down or liquefies the absorbent polymeric materials, thereby releasing the liquid. This is suitably achieved using an agent that disrupts the hydrogen bonding between polymer chains. In preferred embodiments, the agent is or comprises an ionic compound.

Surprisingly, the applicant has found that readily available, non-toxic and inexpensive agents can be used to remove absorbed water trapped within sanitary waste. For example, in preferred embodiments of the invention, the agent is or comprises a salt. Preferred salts include halides of alkali metals. More preferably, the agent is or comprises one or more of sodium chloride, potassium chloride and sodium bicarbonate. Such salts are readily available and, in the Examples disclosed herein, experiments have been conducted using readily available salt-containing products such as table/cooking salt (sodium chloride), reduced sodium cooking salt (a mixture of sodium and potassium chloride sometimes known as "LoSaIt") and different formulations of dishwasher salt (predominantly sodium chloride). Various impurities or other compounds may be present, e.g. iodine or anti-caking agents, which are frequently added to cooking salt.

Sodium chloride is a particularly preferred salt in the context of the present invention due to its availability as an inexpensive bulk commodity, its non-toxicity and its ease of handling. In certain embodiments, the sodium chloride may be obtained from natural sources without extensive processing or purification, e.g. as sea salt or rock salt. The Examples provided herein confirm the efficacy of treatment of waste with sodium chloride and hence the present invention provides a simple and inexpensive route to removal of absorbed water from polymer-containing waste. In view of the surprisingly good results obtained by simple salt treatment, the invention is conveniently carried out using a solution comprising only one dissolved salt, e.g. sodium chloride. Thus, in preferred embodiments, the solute comprises at least 60%, at least 70%, at least 80%, at least 90% or at least 95% of a single salt, such as those disclosed herein.

Alternatively or additionally, a weak acid can be used to disrupt the hydrogen bonds between the polymer chains and promote the release of trapped liquid, Accordingly, in a preferred embodiment the agent comprises a weak acid, e.g. vinegar or citric acid.

Typically, the waste will be treated by soaking it in a solution containing one or more of the preferred agents. For example, in certain embodiments of the invention, the sanitary waste is treated with a salt solution. This provides a convenient treatment step and ensures better penetration of individual items in the waste than is typically achievable by treating waste with a dry salt preparation. Various concentrations of the agent, e.g. the salt solution, can be used. Experiments have been carried out by the applicant using salt concentrations of between 50 grams/litre and 150 grams/litre, and particularly good results have been obtained in the range 100-150 grams/litre. The treatment time can also be varied. In general, the waste will be exposed to the agent, e.g. the salt solution, for at least about 30 minutes, preferably for at least about an hour, and more preferably for about 1-2 hours. In some embodiments exposure of the waste to the agent may be for a time period exceeding 2 hours.

Conveniently, the duration of the exposure of the waste to the agent will be coordinated with the cycle time of the downstream processing steps. For example, when the downstream waste processing is a pyrolysis process, the waste is conveniently exposed to the agent for a time period approximately equal to the cycle time of the pyrolysis step. In other embodiments, the combined duration of the exposure of the waste to the agent and subsequent physical treatment of the waste to extract released liquid is approximately equal to the cycle time of the downstream processing (e.g. pyrolysis) step. This allows downstream processing of one batch of waste while the next batch of waste is being treated to release absorbed water.

The treatment to release absorbed water can conveniently be carried out at ambient temperature, typically at approximately 18-25°C. Alternatively, the treatment can be carried out at elevated temperatures, for example at about 40⁰C or at about 60⁰C. The use of such temperatures may enhance the dissolution of the agent, for example when the agent is a salt, and/or may reduce the treatment time necessary to achieve acceptable levels of water release. Other temperatures, e.g. within the range 18-60⁰C, can readily be selected by the skilled person.

In embodiments in which the treatment is combined with downstream thermal processing such as pyrolysis, the heat generated by the downstream processing can conveniently be used to raise the temperature of the treatment solution. This further enhances the energy efficiency of the process as little or no additional energy input is required to raise the temperature of the treatment solution.

Once the polymer has been disrupted, and the trapped water released, the liquid is preferably removed from the waste. This is typically achieved by incorporating an additional step of physical treatment of the sanitary waste to extract released liquid. This step can be carried out in the same container that is used for the treatment to release absorbed water from the polymer-containing waste. Alternatively, the waste can be transferred to a separate container or apparatus for the physical treatment step. For example the waste can be treated using apparatus as described herein in respect of the fourth aspect of the invention. Various suitable methods are available for separating liquid and solid waste and such methods would be familiar to the skilled person. These methods include, but are not limited to, centrifugation, squeezing, crushing and shredding. In preferred embodiments, the physical treatment comprises crushing and/or shredding the sanitary waste. For example, the waste can be squeezed or pressed using a ram. The released water can then be disposed of in any appropriate manner, e.g. via the sewerage system.

It is preferred that as much water as possible is released from the waste prior to further treatment. In certain embodiments, about 25% or more, about 50% or more, about 75% or more, or about 90% or more of the absorbed water is released and/or separated from the waste. In some cases substantially all of the absorbed water is released and/or separated from the waste. In the hands of the applicant, initial trials have typically resulted in a 40-70% reduction in absorbed water, although further improvements in efficiency can be achieved using permanent, commercial scale apparatus

Following removal of the water, processing of the waste can be carried out using any suitable method available to the skilled person. Such methods include incineration methods and thermal treatment methods such as pyrolysis. Thus, in a preferred embodiment, the method comprises the additional step of pyrolysis and/or combustion of the treated waste. Typically, the waste is heated to a high temperature in a closed vessel, e.g. to a temperature of about 400-700⁰C, and air is subsequently introduced into the vessel. This results in the combustion of the waste, leaving a fine ash as residue. This residue can be removed from the vessel, e.g. by flushing with water and disposed of via the sewerage system. In particularly preferred embodiments, the pyrolysis and/or combustion is carried out using the PyroPure® process described in International patent application no. PCT/GB2007/00853.

The methods and uses of the invention can conveniently be carried out using apparatus e.g. as described according to the fourth aspect of the invention.

When a thermal processing step is included, this results in a process in which the waste is (a) treated to release absorbed water, (b) subjected to physical treatment to extract the water released in step (a), and (c) subjected to thermal processing, e.g. using the PyroPure® apparatus and process. This provides an efficient and coordinated process resulting in destruction of the sanitary waste to yield a waste stream which can safely and conveniently be disposed of via the sewerage system.

In a second aspect the invention provides use of a chemical agent to facilitate and/or enable release of liquid from sanitary waste prior to further processing.

As is the case for the other aspects of the invention, the sanitary waste typically comprises one or more absorbent polymeric materials. In general, the absorbent polymeric materials will comprise one or more hydrophilic non-toxic crosslinked polymers, for example one or more cornstarch-derived polymeric components or synthetic analogues thereof. In preferred embodiments, the absorbent polymeric materials comprise one or more saponified starch-graft polyacetonitrile copolymers.

The agent used in the second aspect of the invention preferably breaks down or liquefies the absorbent polymeric materials, thereby releasing the liquid. Any suitable agent can be used, including the agents described in relation to the first aspect of the invention. Accordingly, the agent may disrupt the hydrogen bonding between polymer chains and may be or comprise an ionic compound.

In preferred embodiments, the agent is or comprises a salt and more preferably the agent is or comprises one or more of sodium chloride, potassium chloride and sodium bicarbonate. A particularly preferred agent is sodium chloride. Alternatively or additionally the agent may comprise a weak acid, e.g. vinegar or citric acid. Various agent concentrations and treatment times can be used, for example as described in relation to the first aspect of the invention. The use of the second aspect of the invention is particularly suitable for the treatment of sanitary waste which comprises items such as nappies and or incontinence pads, e.g. as described in relation to the other aspects of the invention.

As has been noted above, the methods of the first aspect and the uses of the second aspect of the invention permit sanitary waste to be treated in less time and/or with lower energy input that previously possible. Accordingly, in a third aspect, the invention provides a method of improving the efficiency of sanitary waste processing comprising chemical treatment of the sanitary waste to release absorbed liquid prior to further processing.

Typically, the released liquid is removed or separated from the solid waste prior to further processing. This is advantageous because the further processing of the sanitary waste will, in general, comprise heating the sanitary waste and removal of the liquid component of the waste means that time and energy need not be expended in driving off the liquid. As has been described in relation to other aspects of the invention, this can be conveniently achieved in various ways, including removing the released liquid by crushing and/or shredding the sanitary waste.

This step of removing the liquid component of the waste is particularly beneficial when the further processing of the sanitary waste comprises pyrolysis and/or combustion. This is particularly so in preferred embodiments in which the further processing of the sanitary waste comprises heating the sanitary waste to between about 400-700°C, e.g. when the method is carried out using the PyroPure® process, because the retention of liquid in the waste increases the time and energy required to bring the waste to the treatment temperature.

In the hands of the applicant, implementation of the methods of the invention has resulted in the process time being reduced relative to a process not comprising chemical treatment of the sanitary waste. The methods of the invention have also resulted in the energy usage being reduced relative to a process not comprising chemical treatment of the sanitary waste. For example, initial experiments conducted by the applicant have shown that a reduction of about or in excess of 50% of the thermal processing time can be routinely achieved. The same experiments also achieved reductions of energy expenditure of approximately 30 to 60%.

It will be appreciated that the methods of the third aspect of the invention can be carried out on sanitary waste comprising polymeric materials of the types described in relation to the other aspects of the invention. Similarly, the chemical treatment of the sanitary waste can be carried out using any one or more of the agents described in relation to the other aspects of the invention.

In certain circumstances, it may not be possible to carry out all processing steps at the same location and the waste may need to be transported to a remote site for further processing. In such circumstances, the invention can advantageously be used to reduce the weight of waste prior to transportation. For example, the waste can be treated with an agent (e.g. by soaking in a salt solution) and the released water can be removed, preferably by shredding or crushing the waste. The released water can then be disposed of via the sewers and the solid waste can be transported to the remote site. Given that sanitary products can absorb up to 400-800 times their weight in water, this processing step can significantly reduce the weight of the waste prior to transportation and hence can result in further improvements in efficiency in the form of reduced transport costs and fuel usage.

The methods and uses of the preceding aspects of the invention can conveniently be carried out using the apparatus of a fourth aspect of the invention, which provides an apparatus for treating sanitary waste to release absorbed liquid prior to further processing comprising a first chamber, wherein the first chamber is adapted to receive sanitary waste and a chemical agent, wherein exposure of the sanitary waste to the agent facilitates and/or enables release of absorbed liquid.

The apparatus may optionally comprise a second chamber adapted to receive waste from the first chamber and adapted for the execution of physical processing to extract liquid released from the waste as a result of treatment of the waste with the chemical agent. In embodiments in which the second chamber is absent, such physical processing can be carried out in the first chamber. In either case, the physical processing can carried out using the methods described herein, e.g. by centrifugation, squeezing, crushing and/or shredding of the waste. In preferred embodiments, the second chamber or, if the second chamber is not present, the first chamber, is provided with means for squeezing, crushing or pressing the waste to extract released liquid. In preferred embodiments, the apparatus is provided with a ram to effect the step of extracting released liquid.

Typically the first chamber and the second chamber, if present, will comprise an outlet by means of which extracted liquid and/or the used chemical agent can be disposed of, e.g. to the sewerage system.

In preferred embodiments, the apparatus is integrated with a downstream thermal processing apparatus, for example a pyrolysis apparatus such as the PyroPure® apparatus described herein and in PCT/GB2007/00853 (the contents of which are incorporated herein by reference). Thus, in a preferred embodiment, the apparatus comprises a first chamber for treatment of sanitary waste with a chemical agent to release absorbed liquid, a second chamber in which the released liquid is physically extracted from the waste, and a further chamber in which pyrolysis is effected. As has already been noted, the further chamber is generally provided with an outlet by means of which the residue can be disposed of, e.g. by flushing the further chamber with water or superheated steam after the pyrolysis and combustion of the waste has been effected.

Typically, the apparatus is also provided with means to transfer the waste mechanically between the first and second chambers, the second and further chambers or, in embodiments in which the optional second chamber is absent, between the first and further chambers. A number of suitable means are known and readily available to the skilled person. However, in preferred embodiments, the waste is transferred between chambers using an auger.

Thus, in preferred embodiments of the invention, the treatment of sanitary waste is carried out in an integrated manner in which the water content of the waste is significantly reduced prior to pyrolysis. This in turn results in reductions in the thermal processing time of the pyrolysis step, the energy expenditure, or both, as has been discussed e.g. in relation to the third aspect of the invention.

It will be appreciated that in such an integrated apparatus and in the methods and uses that are carried out using the apparatus, that the batch size for each processing step is scaled to suit the batch size of the final processing step. For example, when the final processing step uses the PyroPure® apparatus, the batch size is preferably 8 kg or less. Of course, the prior steps result in the release of significant quantities of absorbed water and hence the prior processing steps can be carried out on significantly larger batches. Thus, the first and optional second chambers can be adapted to receive batches of the appropriate size.

Once the efficiency (i.e. the % reduction in waste weight) of the pre-pyrolysis steps of any embodiment of the invention is known, then the appropriate batch size for the pre-pyrolysis steps can readily be calculated. By way of example, when the methods of the invention provide a 50% reduction in the weight of the sanitary waste, through release and extraction of absorbed water, the pre- pyrolysis steps and the first and second chambers can suitably process batches of up to 16 kg. Similarly, when the pre-pyrolysis steps result in a 75% reduction in the weight of the sanitary waste, the batch size for the pre-pyrolysis steps can be up to 32 kg. The invention is further described in the following example.

Example 1

Objective:

Experiments were performed in order to determine whether the time and power consumption for destroying varying loads of nappies and incontinence pads can be reduced by chemical treatment followed by physical treatment to eliminate liquid prior to the start of the thermal process. In the experiments described herein loads of nappies and incontinence pads were first treated by soaking the load in a salt solution followed by mechanical squeezing to eliminate the liquid prior to the start of the thermal process, which was carried out using PyroPure® apparatus.

Baseline Experiment:

A baseline experiment was carried out using a known weight of wet nappies and incontinence pads but no pre treatment. This gave the cycle time and power consumption for untreated waste.

Test experiments:

Test loads of wet nappies and incontinence pads were soaked in varying concentrations of different saline solutions for differing periods of time. Following the period in soak the nappies and pads were squeezed and reweighed before being placed into the PyroPure® chamber. The cycle time and power consumption for destruction were recorded for each load.

Experimental Material:

• A mixture of eight Nappies and Incontinence Pants were used for each test. Each load consisted of different products and sizes within the load, but the overall composition of each load was identical.

• The composition of each load was as follows: o UniChem® Disposable Incontinence Double Pad (x1) o Tesco® Value Unisex Nappy Junior 14-25Kg (x1) o Pampers Baby Dry® Nappy, size 6 Extra Large (x2) o Tesco® Super Fit Nappy size 4+ (x2) o Tesco® Baby Essentials Ultra Dry size 4 Maxi (x2) « 4 litres of water were used for each test.

• Salt solutions were prepared using standard tap water and one of the following commercially available salt compositions: o Sodium chloride (NaCI)- Tesco® Cooking Salt o Potassium chloride (KCI)/sodium chloride (NaCI) 66%/33% mixture - "LoSalt®" Reduced Sodium Salt o Dishwasher salt, 99% purity - "Finish®" brand o Dishwasher salt Granules - "Tesco®" brand

Unit Preparation:

All experiments were conducted using a PyroPure® unit (designated the PP2 unit) having a 130 litre chamber with external heaters attached to a filtration system which comprises a water scrubber, ceramic filters, activated carbon and a catalytic converter. The PyroPure® apparatus was prepared and used as follows: • All debris was removed from the chamber before each test.

• An additional grid at the bottom of the chamber was installed to prevent small particles falling to the base of the chamber.

• The filtration system excluded the ceramic wands except in Tests 5 & 16 when a new system was used to test whether by heating the air around the wands more efficient filtration was achieved.

• The Blower was set to 2500rpm and the Extraction to 30Hz.

• The test temperature was ramped up using the standard ramp.

• All tests were performed at room temperature.

Baseline Test:

Test No. 1:

• Eight nappies/pads were each soaked with approximately 0.5 litres of water. The total water use equalled 4 litres. The product was allowed to stand for approximately one hour to ensure that the product had fully absorbed the water. The total weight was then recorded

• The product was then placed between two boards one item at a time and compressed in a vice to the driest possible state without bursting the gel compartment.

• The total weight was recorded and the load was then placed in the PyroPure® chamber evenly distributed over the grid in different orientations. • Cycle time, time settings and temperature settings were recorded together with any residue left at the end of the test. Any residue left was bagged. Tests 2 -17:

• The load was saturated with 4 litres of water, approximately 500 ml of water per nappy/incontinence pad. The saturated load was allowed to stand for a minimum of one hour. The total start weight was recorded.

• The load was then placed in a bath of salt water, the concentration of the saline solution and time in bath was dependent on the test being run.

• After the specified period the load was removed from the bath, placed between two boards one at a time and compressed in a vice to the driest possible state without bursting the gel compartment. The final weight was recorded.

• The load was then placed in the PyroPure® chamber evenly distributed over the grid in different orientations

• The run was performed with all parameters and results being recorded as indicated in Tables 1 and 2.

Shredded Nappy/Pad Comparison Test:

Test No. 18:

• Eight Nappies/Pads were soaked with approximately 0.5 litres of water. Total water use equalled 4 litres. All of the nappies/pads were cut and pulled apart.

• The total weight was recorded and the load was evenly distributed over the grid in the PyroPure® chamber.

• The test temperature was ramped up using the standard ramp.

• Time and temperature settings were recorded together with the total cycle time.

• Any residue was recorded and bagged at the end of the test. Table 1 - Details of Tests 2 -17

Test No. Salt Type Concentration Time in Salt Bath

2 Cooking 50g/litre 1 Hour

3 Cooking 100g/litre 1 Hour

4 Cooking 150g/litre 1 Hour

5 Cooking 50g/litre 2 Hours

6 Cooking 100g/litre 2 Hours

7 Cooking 150g/litre 2 Hours

8 LoSaIt 50g/litre 1 Hour

9 LoSaIt 100g/litre 1 Hour

10 LoSaIt 150g/litre 1 Hour

11 LoSaIt 50g/litre 2 Hours

12 LoSaIt 100g/litre 2 Hours

13 LoSaIt 150g/litre 2 Hours

14 Finish 100g/litre 1 Hour

15 Finish 100g/litre 2 Hours

16 Granules 100g/litre 1 Hour

17 Granules 100g/litre 2 Hours

Table 2 - Test Results

Key:

Cooking 1 Sodium Chloride (NaCI) Salt - Tesco® Cooking Salt

LoSaIt 2 Potassium (KCI) 66%/Sodium (NaCI) 33% Salt - "LoSalt®" Reduced Sodium Salt

Finish 3 Dishwasher Salt, 99% purity

Granules 4 Dishwasher Salt Granules - "Tesco®" brand

Conclusions

1 The addition of even a low concentration of salt significantly increased the amount of water reduction achieved. 2 The optimum concentration is between 100 and 150 grams/litre.

3 The type of salt used did not significantly influence the results achieved but the highest percentage water reduction, 72.2%, was achieved with 150grams/litre of 'LoSaIt'.

4 There was a significant reduction in both power consumption and time for all pre-treated loads. The untreated load took 3hrs 24 mins compared to between 1 hr 21 mins to 1hr 55 mins for the treated loads.

5 Power consumption was also lower following treatment, with the untreated consumption of 22.908KWh falling to between 9.913 and 15.855KWh following treatment. These figures may be further improved in use, as permanent apparatus, e.g. on a commercial scale, will be more efficient than the test apparatus used for the present experiments. However the data presented here clearly indicates the benefits of using salt to break down the polymer.

The invention hence provides methods for processing sanitary waste, use of chemical agents to facilitate such processing, and methods for improving the efficiency of such processing.

Claims

1. A method for processing sanitary waste comprising the step of chemical treatment of the waste to release liquid present therein prior to further treatment of the waste.

2. A method according to claim 1, wherein the sanitary waste comprises one or more absorbent polymeric materials.

3. A method according to claim 2, wherein the absorbent polymeric materials comprise one or more hydrophilic non-toxic crosslinked polymers.

4. A method according to claim 2 or claim 3, wherein the absorbent polymeric materials comprise one or more cornstarch-derived polymeric components or synthetic analogues thereof.

5. A method according to any of claims 2 to 4, wherein the absorbent polymeric materials comprise one or more saponified starch-graft polyacetonitrile copolymers.

6. A method according to any of claims 2 to 5, wherein the sanitary waste is treated with an agent that breaks down or liquefies the absorbent polymeric materials, thereby releasing the liquid.

7. A method according to claim 6, wherein the agent disrupts the hydrogen bonding between polymer chains.

8. A method according to claim 6 or claim 7, wherein the agent is or comprises an ionic compound.

9. A method according to any of claims 6 to 8, wherein the agent is or comprises a salt.

10. A method according to claim 9, wherein the agent is or comprises one or more of sodium chloride, potassium chloride and sodium bicarbonate.

11. A method according to any of claims 6 to 10, wherein the agent is or comprises sodium chloride.

12. A method according to any of claims 6 to 11 , wherein the agent comprises a weak acid, e.g. vinegar.

13. A method according to any of claims 2 to 12, comprising treating the sanitary waste with a salt solution.

14. A method according to any preceding claim comprising the additional step of physical treatment of the sanitary waste to extract released liquid.

15. A method according to claim 14, wherein the physical treatment comprises crushing and/or shredding the sanitary waste.

16. A method according to any preceding claim, comprising the additional step of pyrolysis and/or combustion of the treated waste.

17. A method according to claim 16, wherein the waste is heated to a temperature of about 400-700⁰C.

18. A method according to claim 17 or claim 18, wherein the pyrolysis and/or combustion is carried out using the PyroPure® process.

19. A method according to any preceding claim for processing of nappies and or incontinence pads.

20. Use of a chemical agent to facilitate and/or enable release of liquid from sanitary waste prior to further processing.

21. Use according to claim 20, wherein the sanitary waste comprises one or more absorbent polymeric materials.

22. Use according to claim 21 , wherein the absorbent polymeric materials comprise one or more hydrophilic non-toxic crosslinked polymers.

23. Use according to claim 21 or claim 22, wherein the absorbent polymeric materials comprise one or more cornstarch-derived polymeric components or synthetic analogues thereof.

24 Use according to any of claims 21 to 23, wherein the absorbent polymeric materials comprise one or more saponified starch-graft polyacetonitrile copolymers.

25. Use according to any of claims 21 to 24, wherein the agent breaks down or liquefies the absorbent polymeric materials, thereby releasing the liquid.

26. Use according to claim 25, wherein the agent disrupts the hydrogen bonding between polymer chains.

27. Use according to any of claims 20 to 26, wherein the agent is or comprises an ionic compound.

28. Use according to any of claims 20 to 27, wherein the agent is or comprises a salt.

29. Use according to claim 28, wherein the agent is or comprises one or more of sodium chloride, potassium chloride and sodium bicarbonate.

30. Use according to any of claims 20 to 29, wherein the agent is or comprises sodium chloride.

31. Use according to any of claims 20 to 30, wherein the agent comprises a weak acid, e.g. vinegar.

32. Use according to any of claims 20 to 31 , wherein the sanitary waste comprises nappies and or incontinence pads.

33. A method of improving the efficiency of sanitary waste processing comprising chemical treatment of the sanitary waste to release absorbed liquid prior to further processing.

34. A method according to claim 33, wherein the released liquid is removed prior to further processing.

35. A method according to claim 33 or 34, wherein the further processing of the sanitary waste comprises heating the sanitary waste.

36. A method according to any of claims 33 to 35, wherein the further processing of the sanitary waste comprises pyrolysis and/or combustion.

37. A method according to any of claims 33 to 36, wherein the further processing of the sanitary waste comprises heating the sanitary waste to between about 400-700⁰C.

38. A method according to any of claims 33 to 37, wherein the further processing is carried out using the PyroPure® process.

39. A method according to any of claims 33 to 38, wherein the process time is reduced relative to a process not comprising chemical treatment of the sanitary waste.

40. A method according to any of claims 33 to 39, wherein the energy usage is reduced relative to a process not comprising chemical treatment of the sanitary waste.

41. A method according to any of claims 33 to 40, wherein the sanitary waste comprises one or more absorbent polymeric materials.

42. A method according to claim 41 , wherein the absorbent polymeric materials comprise one or more hydrophilic non-toxic crosslinked polymers.

43. A method according to claim 41 or claim 42, wherein the absorbent polymeric materials comprise one or more cornstarch-derived polymeric components or synthetic analogues thereof.

44. A method according to any of claims 41 to 43, wherein the absorbent polymeric materials comprise one or more saponified starch-graft polyacetonitrile copolymers.

45. A method according to any of claims 41 to 44, wherein the chemical treatment uses an agent that breaks down or liquefies the absorbent polymeric materials, thereby releasing the liquid.

46. A method according to claim 45, wherein the agent disrupts the hydrogen bonding between polymer chains.

47. A method according to claim 45 or claim 46, wherein the agent is or comprises an ionic compound.

48. A method according to any of claims 45 to 47, wherein the agent is or comprises a salt.

49. A method according to claim 48, wherein the agent is or comprises one or more of sodium chloride, potassium chloride and sodium bicarbonate.

50. A method according to any of claims 45 to 49, wherein the agent is or comprises sodium chloride.

51. A method according to any of claims 45 to 50, wherein the agent comprises a weak acid, e.g. vinegar.

52. A method according to any of claims 33 to 51 , comprising treating the sanitary waste with a salt solution.

53. A method according to any of claims 33 to 52, wherein the released liquid is removed by crushing and/or shredding the sanitary waste.

54. An apparatus for treating sanitary waste to release absorbed liquid prior to further processing comprising a first chamber, wherein the first chamber is adapted to receive sanitary waste and a chemical agent, wherein exposure of the sanitary waste to the agent facilitates and/or enables release of absorbed liquid.

55. An apparatus according to claim 54, further comprising a second chamber adapted to receive waste from the first chamber and adapted for the execution of physical processing to extract liquid released from the waste.

56. An apparatus according to claim 54, wherein the first chamber is adapted for the execution of physical processing to extract liquid released from the waste.

57. An apparatus according to any of claims 54 to 56, wherein the chemical agent is a salt solution.

58. An apparatus according to any of claims 54 to 57, comprising a further chamber in which pyrolysis is effected.