Sanitary waste: odor and contaminant abatement with multistep hybrid system

The treatment of medical waste can involve several issues, including those related to odorigenic emissions.

This is what was also happening to a company in central Italy that specializes in the collection, storage and sterilization of biohazardous medical waste, whose waste treatment plant was experiencing significant odorigenic issues resulting, in particular, from the sterilization process.

Complaints from residents near the facility continued to mount. The plant operator then decided to contact us to help solve the odorigenic emission problem.

After an initial analysis of the sanitary waste treatment plant and the possible sources of odor nuisance, we took it upon ourselves to design and implement a customized multistep plant to treat the malodorous emissions and prevent them from spreading to the surrounding area.

Our technology enabled us to achieve an odor and contaminant abatement efficiency of more than 85%.

We have intervened with our new plant design and implementation service and have:

• studied the emission problem at the production site;
• designed and installed the new plant;
• verified the abatement efficiency.

Let's look at each stage of this project in detail, starting with the characteristics of the existing plant.

The plant treats sanitary solid waste collected from hospital facilities, as well as the containers used for collection itself and storage, for the purpose of energy valorization. It consists of:

• loading and shredding;
• sterilization;
• air circuit;
• effluent emission.

In Italy, the technical reference standard for the management of "medical waste" is Presidential Decree No. 254/2003, which indicates two possible disposal strategies for hazardous waste with infectious risk:

• sterilization
• or incineration.

Sterilization is defined as "...abatement of the microbial load such as to ensure an S.A.L. (Sterility Assurance Level) of not less than 10-6. Sterilization shall be carried out in accordance with UNI 10384/94, part one, by a process that also includes shredding and drying for the purpose of non-detectability and greater effectiveness of the treatment, as well as the decrease in volume and weight of the waste itself" (Presidential Decree No. 254/2003 - Art.2, letter m).

The sterilization process of the plant in question is delegated to a closed-circuit heat treatment with its own emission.

Specifically, the sterilizer consists of:

• a sterilization chamber equipped with a double jacket for the circulation of oil or steam;
• a paddle shaft that rotates at a speed to agitate the material and bring it into contact with the inner wall of the sterilization chamber for a minimum time necessary for sterilization.

The steam formed inside the sterilizer - corresponding to the water evaporated during drying - is automatically extracted from the closed sterilization circuit. 

Sanitary solid waste, after being collected and stored in the appropriate containers, is shredded and subjected to steam treatment at 150°C to make it chemically and biologically non-hazardous.

This sterilization treatment was a source of foul odors that leaked into the areas surrounding the plant, causing odorigenic problems for the people living in the surrounding area.

The problem analysis phase allowed us to present the most suitable proposal to the client that could meet the expectations and olfactometric requirements.

After careful verification of the areas to be treated and technical feasibility, we proposed to install a multistage DKFil® dry filtration and osmogenic barrier system for olfactory mitigation and abatement of ammonia and VOCs in storage activities.

Our solution for the abatement of chemical contaminants in treatment activities involved the extraction of indoor air from the appropriately compartmentalized building where incoming and post-treatment materials are stored.

The following abatement process was decided to be followed for the treatment of atmospheric input:

• aeriform capture and conveyance;
• condensate separation;
• physical/chemical adsorption of pollutants;
• olfactometric finishing;
• extraction by centrifugal fan;
• venting of the mitigated aeriform into the atmosphere via stack.

1. Capture and conveyance of emissions

Emissions are captured within a subdivision by a special system and conveyed to the treatment plant by suitable connecting pipes.

2. Separation of condensate - Demister

Separation of the condensed-phase fraction (water, oil, nonvolatile solvents present due to entrainment and transport) in the aeriform stream is done internally in the filter by means of pall rings.

The condensed phase, once separated from the aeriform phase, is collected at the bottom of the unit and discharged by means of a shutoff valve.

The demister unit is provided internal to the DKFil® so as to limit the footprint.

3. Physical and chemical adsorption of pollutants in the aeriform - DKFil®

The aeriform odor mitigation process takes place within the DKFil® dry filter unit, which is sized and designed according to the flow rate of the aeriform to be treated and the chemical and physical characteristics of the odorigenic molecules to be removed.

The filter system consists of a static bed composed of multiple adsorbent and chemically reactive layers that operate selectively and synergistically against the different substances present in the aeriform effluent being treated.

The removal of contaminant gases occurs according to thermodynamically irreversible processes under standard operating conditions.

4. Zephiro UTS olfactometric finishing system.

The Zephiro UTS system is an innovative distribution system using ultrasonic aerodispersion technology. This system can be housed adjacently to the DKFil® dry filtration unit.

The olfactometric finishing system consists of:

• a storage tank,
• an ultrasonic transducer with associated floating support
• an electrical command and control panel
• dosing unit.

The dispensing cycle involves the entry of mains water to the system and subsequent dosing of the neutralizing product.

The ultrasonic transducer, placed inside the 'tank, suspended at a certain level from the free surface of the liquid, will produce a mist of neutralizing product, impalpable composed of very fine particles between 5 and 10 microns.

The high micronization of the neutralizing product will allow an increase in the overall efficiency of the plant in terms of odor emission abatement by neutralizing the emission with the evaporated product.

5. Suction by centrifugal fan

6. Release of the mitigated aeriform into the atmosphere via chimney

The system was installed and started up directly by our trained technicians.

In the testing phase, olfactometric measurements were conducted that demonstrated abatement efficiencies exceeding 85%.

The multistage system installed by Labiotest ensures that odor nuisance is reduced and that odorous emissions do not imply risks to humans and the environment. It was also adapted to the critical technical issues of the case, and both the investment and maintenance costs were proportionate to the actual needs of the client