II. TYPES OF HOSPITAL WASTEWATER

Wastewater produced by hospitals and by hospital-related industries originates from many sources. The Technology Identification Subgroup assigned the various medical industry wastewater streams into the following four categories:

• wastewater from Clinical Laboratories.
• wastewater from Research Laboratories.
• wastewater from Medical Waste Incinerators equipped with fume scrubbers.
• wastewater from Hospital Laundries.

To understand the characteristics of these wastestreams and the difficulties that might be encountered when attempting their pretreatment, it is important to understand the operations or sources of waste that contribute pollutants to the individual wastestreams. In this way, the chemical constituency of each wastestream can be predicted and potential interferences in a mercury removal process can be anticipated.

The following are brief overviews of typical wastewater-producing processes in each category of hospital facility. Each overview includes an interpretation of the analytical data generated from a wastewater sampling and analyses project that was performed at a representative facility. The wastewater sampling and analysis project was performed by a subgroup of the Phase II Work Group known as the Wastewater Characterization (WWC) Subgroup. Refer to the next section of this report for a summary of the WWC Subgroup project.

Clinical Laboratories:

Most clinical laboratories perform a wide range of services but not every clinical laboratory is the same. Some clinical laboratories are independent of hospitals. Generally, the larger the hospital, the greater the extent of services offered by the clinical laboratory.

The types of processes performed in a clinical laboratory can include: anatomic pathology (including routine histology and cytology), chemistry, drug monitoring and toxicology, hematology, immunology and serology, microbiology, transfusion medicine, and urinalysis. In addition, there can be cytogenetics, flow cytometry, histocompatibility testing, molecular pathology, mycology, and nuclear medicine.

Wastewater from a "typical" clinical laboratory could contain ionic mercury and organomercuric compounds, other heavy metals, organic chemicals, blood products and body fluids, formaldehyde, buffers, dilute mineral acids/bases, phosphates, oxidizers, oil & grease, and particulate materials. Data from the Work Group’s Wastewater Characterization Study suggests that clinical laboratory wastewater would have higher biochemical demand (BOD) and chemical oxygen demand (COD) than domestic sewage. Because there is usually some standardization of work, the wastewater from a specific clinical laboratory may be somewhat consistent in quality and characteristics over long periods.

Research Laboratories:

Perhaps the most diverse and unpredictable wastestreams are those discharged from research laboratories. Many medical institutions are conducting "cutting edge" studies in infectious disease control, blood chemistry, pathology, animal research and inorganic chemistry. Wastes may be produced in significant quantities for short periods or not at all for extended periods. Research laboratory facilities in hospitals can range from one to two laboratory sinks that produce "tens of gallons" each day to hundreds of sinks and related fixtures generating waste volumes in excess of fifty thousand gallons per day.

Wastes can originate from either automated instrumentation or from manual processes and may contain the following pollutants: oxidizers (disinfecting media such as bleach, iodine, peroxides, etc.), radionuclides, proteins (tissue and immunodiagnostics), oil & grease (from vacuum pumps and other rotating equipment), heavy metals (analytical reagents), organic solvents, blood products and other body fluids (urea is a well-known chelator of heavy metals), formaldehyde, phosphates and detergents (from glass cleaning and instrument sterilizing processes), and photographic imaging chemicals (desilvered spent fixer and developer solutions). Data from the Work Group’s Wastewater Characterization Study suggests that (BOD) and (COD) are lower than for clinical laboratories but above average compared with domestic sewage.

Medical Waste Incinerators:

Federal and State regulations closely govern the management of infectious medical or "Red Bag" wastes. Some facilities, trying to reduce the cost of offsite waste disposal, have chosen to install on-site medical waste incinerators to burn these wastes. Air quality regulations typically require the installation of emission controls on the incinerator stacks for particulate and oxides of nitrogen (NO_x) and sulfur (SO_x). Most control systems involve a fume scrubber where pollutants are scrubbed from the waste gas stream into a recirculating water stream. To limit the concentration of pollutants in the recirculating water, part of the water is typically discharged into a sewer system and is replaced with fresh water.

Mercury in the waste gas stream can originate from the waste being burned and also from the fuel used to burn the waste. Red Bag wastes may contain tissue, paper, saturated sorbents, plastics, mercury thermometers, and metallic objects. In some facilities, various animal or human tissues may be disposed of as Red Bag wastes. The liquid wastestream from the incinerator scrubber usually has relatively low concentrations of organic material, oxidizers, but can contain significant concentrations of particulate matter and heavy metals (including mercury). BOD and COD concentrations for incinerator wastewater are usually lower than those of domestic sewage.

Hospital Laundries:

Hospital laundries typically process linens, gowns and lab coats that will contribute a certain amount of organic material, fats, oils and grease (FOG) and an alternating range of pH (alkaline detergent followed by an acidic sanitizer) to the wastestream. This is notably different from a commercial laundry that will commonly process garments, uniforms, wipers, mops and mats often contaminated with heavy metals and petroleum products. Depending upon the processes employed, the hospital laundry wastestream can have elevated temperatures and pH extremes and can contain starch, particulate (including lint), proteins (blood products), detergents, and oxidizers (bleach or other disinfectant). BOD and COD concentrations from laundry wastewater are usually in the normal range for domestic sewage.