The solid waste hazards are well known in the wastewater treatment industry. But it appears that few extensive studies have been conducted on potential airborne and surface hazards. This article describes work my company, Industrial Safety Solutions, completed at a California wastewater plant in response to the client’s request to assess airborne and surface Hepatitis A (HAV) and bacteria (endotoxins) throughout the treatment facility. The project yielded several insights about best practices for protecting workers at wastewater plants. WASTEWATER TREATMENT PROCESS​ The plant processes approximately eight million gallons of wastewater a day from homes and businesses. It uses a tertiary treatment with a combination of physical, chemical and biological processes to remove contaminants. Sludge, or biosolids, is the unavoidable end-product of the wastewater process.

Primary treatment involves screening, clarification, and sedimentation. This is achieved through use of a series of screens and grit-removal clarifiers referred to as “headworks.” Secondary treatment removes dissolved and suspended biological matter by using indigenous, waterborne microorganisms in a managed habitat, such as aeration tanks and settling ponds. Tertiary treatment offers enhanced clarity, filtration, and disinfection through the use of reverse osmosis or media and gravity filtration. Sludge is dewatered in the biosolids building in drying beds and large centrifuges. The end product can be recycled as fertilizer. The treated water leaves the wastewater plant in purple pipes as recycled water to irrigate parks, golf courses, school fields, and cemeteries. 

At the time of our study, HAV air monitoring had not been conducted. In collaboration with the analytical laboratory, we developed a new technique for conducting these measurements. The monitoring was intended to determine whether a PPE hazard assessment and current administrative control procedures, including vaccinations, were adequate to protect employees from possible exposures. There were two key questions we sought to answer: had HAV and bacteria become airborne, and could HAV be found on surfaces throughout the facility? SAMPLING FOR BACTERIA (ENDOTOXINS) According to the Textbook of Bacteriology, the term “endotoxin” applies to any cell-associated bacterial toxin. It properly refers to the lipopolysaccharide complex and can be associated with the outer membrane of Gram-negative pathogens such as Escherichia coli, Salmonella, Shigella, Pseudomonas, Neisseria, Haemophilus influenzae, Bordetella pertussis, and Vibrio cholera. (“Gram-negative” bacteria are those that can be identified via the Gram staining method of bacteria differentiation. Gram stain tests target the cell walls of bacteria.) Many of these Gram-negative bacteria have been associated with foodborne illness and may cause diarrhea, fever, cramps, vomiting, headaches, weakness, or loss of appetite. In severe cases, hospitalization may be necessary. 

Our approach collected bacteria (endotoxin) samples using sterile Endotoxin cassettes, which were analyzed in the laboratory by kinetic chromogenic method analysis. The results were provided in endotoxin units (EU). Personal and area samples were collected from the aeration base, clarifier, equalization channel (EQ), ultraviolet channel (UV), outside the biosolids building, and drying beds. Personal air samples were collected for the duration of the employees’ shift. Area samples were collected on catwalks or platforms above the area of concern and simulated the amount of time workers typically spend in the location. SAMPLING FOR HEPATITIS A The Centers for Disease Control and Prevention (CDC) states that HAV is an acute, contagious liver disease that can range in severity from a mild illness lasting a few weeks to a severe illness lasting several months with an incubation period of approximately 28 days. HAV replicates in the liver and is shed in high concentrations in feces from two weeks before to one week after the onset of clinical illness. Hepatitis A is usually spread when a person ingests fecal matter from contact with objects, food, or drinks contaminated by the feces, or stool, of an infected person. The infection is considered a self-limited disease and does not result in chronic infection or chronic liver disease.

HAV area air samples were collected on catwalks or platforms above working areas including the biosolids building, aeration tanks, clarifiers, inlet channels, and headworks. Wipe samples were collected in areas routinely used by employees including door and bin handles along with steering wheels. The laboratory analyzed the samples by molecular real-time polymerase chain reaction (RTPCR). Results were provided as negative or positive.