Medical or biomedical waste treatment techniques which minimize the formation and release of chemicals or hazardous emissions should be given priority over other technologies. A general description of different treatment processes (low-heat thermal, chemical based, and open burning) can be found in the following section, the majority of current available health care waste treatment options are covered, grouped as follows:

 

  1. Preferred options: Technologies in accordance with International Conventions
  • Low-heat thermal-based processes

– Autoclaves

– Vacuum autoclaves without shredder

– Autoclaves with integrated shredder

– Microwave-based technologies

– Frictional heat treatment

  • Chemical-based processes

– Sodium hypochlorite-based technologies

  • Incineration with flue gas treatment

 

  1. Interim solutions: Technologies used to incrementally improve practices and move towards meeting international standards
  • Automated pressure pulsing gravity autoclaving
  • Dual and single chamber incinerators
  1. Last resort option: Where there are no alternative treatment options
  • Burning in a pit and open burning

 

                                                    Treatment technologies ladder

 

1.1 Low-heat based processes

1.1.1 Autoclaves

An autoclave consists of a metal vessel designed to withstand high pressures, with a sealable door and an arrangement of pipes and valves through which steam is introduced into and removed from the vessel. Because air is an effective insulator and a key factor in determining the efficiency of steam treatment, removal of air from the autoclave is essential to ensure penetration of heat into the waste. Waste treatment autoclaves must also treat the air removed at the start of the process to prevent pathogenic aerosols from being released. This is usually done by treating the air with steam or passing it through a specific filter (e.g. High Efficiency Particulate Air (HEPA) filter or microbiological filter) before being released. The resulting condensate must also be decontaminated before being released to the waste water system.

 

1.1.1.1 Vacuum autoclaves

Modern waste autoclaves use a vacuum pump and/or a steam ejector to evacuate air before introducing steam, to ensure safe decontamination of the waste. One option is pre-vacuum autoclaves, which evacuates air once before injecting steam. Autoclaves which use a fractionated vacuum process to remove air are a safer option. This process evacuates air and admits steam several times to ensure that as much air as possible from the chamber is removed so that there is better steam penetration in the waste and better homogeneity of temperature during the decontamination phase . A drying phase after treatment is added to protect the operator against steam when opening the door. Waste is decontaminated at 121 °C to 134 °C therefore the waste bags used in autoclaves must be heat resistant and must allow steam to enter the bag. Polyethylene bags – the most widely available type – can resist 121 °C, but polypropylene bags are needed for machines operating at 134 °C. After treatment, the waste is considered non-hazardous and can be disposed accordingly.

Vacuum autoclave

 

Pre-vacuum process                                Fractionated vacuum process

The use of vacuum autoclaves includes the following advantages:

  • Low environmental impacts
  • No hazardous residues
  • Complies with Stockholm convention
  • Some treated wastes can be recycled

 

1.1.1.2 Autoclaves with integrated shredding

Autoclaves with integrated grinding or shredding are steam-based systems, which have been developed to improve the transfer of heat into waste, achieve more uniform heating of waste, render the waste unrecognisable and/or make the treatment system a continuous process. These systems are sometimes referred to as advanced autoclaves, hybrid autoclaves or advanced steam treatment technologies (WHO 2014). Pre-shredding allows better steam penetration and efficacy. The process might also include pre-vacuum or fractionated vacuum phase for extra safety. At the end of the cycle, the waste is considered non-hazardous and can be disposed accordingly. Some waste may also be suitable feedstock for recycling.

The use of autoclaves with integrated grinding or shredding has the following advantages and disadvantages:

  • Low environmental impacts
  • No hazardous residues
  • Complies with Stockholm convention
  • Reduction of volume
  • Residue is unrecognizable

 

Capacities of autoclaves with integrated shredding range from 5 to 3000 kg/hour. The cycle time includes the time needed for complete treatment including adding waste, shredding, steam exposure, and waste removal. The tables below provide some examples of capacities and consumption for autoclaves using a built in steam generator and an external steam source. The data are approximate and based on maximum load capacity per cycle, and with standard configuration of parameters.

 

1.1.2.1 Batch wise microwaves

A typical batch wise microwave system treats waste in batches in a closed waste decontamination unit. Some units require special reusable, fully enclosed, microwavable containers in which the waste is collected beforehand. Microwave systems may have multiple programmable cycles corresponding to different treatment temperatures or levels of disinfection.

The use of batch wise microwaves for the treatment of infectious and sharp waste includes the following advantages and disadvantages:

  • Low environmental impacts
  • No hazardous residues
  • Complies with Stockholm Convention

 

Microwaving is an environmental friendly technology. Waste water is decontaminated during the process. Air emissions from microwave units are minimal. There are no pollutant emission limits specific for microwaves.

 

 

Capacities and consumption

Batch wise microwave systems range in capacity from 1 to 210 kg per hour. The cycle time includes the time needed for adding waste, processing, and waste removal.

 

 

4.1.2.2 Continuous Microwave Technologies

A typical continuous microwave system consists of an automatic charging system, hopper, shredder, conveyor screw, steam generator, microwave generators, discharge screw and controls. The equipment includes hydraulics, HEPA filter and microprocessor-based controls. Waste bags are introduced into the hopper where steam may also be injected. To prevent the release of airborne pathogens, air is extracted through a HEPA filter as the waste bags are loaded. After the hopper lid is closed, waste goes through a shredder. The waste particles are conveyed through a large metal auger (conveyor screw) where they are further exposed to steam and heated to 100°C by several microwave generators. Waste is then kept in a holding section where medical wastes are maintained at 100°C for 50 minutes.

The use of continuous microwaving technology includes the following advantages and disadvantages:

  • Low environmental impacts
  • Residue is non-hazardous
  • Complies with Stockholm Convention
  • Residue is unrecognizable
  • Reduction of waste volume

 

Microwaving is an environmentally friendly technology. Waste water is decontaminated through the process. Air emissions from microwave units are minimal. There are no pollutant emission limits specific for microwaves. The system needs to be completely enclosed to prevent emission of aerosols during the waste shredding process.

Continuous microwave technologies are available in the range of 100 to 800 kg per hour.