Introduction 

Wastewater is a diverse mixture of microorganisms from human and animal excreta, food production, and industrial input. Although treatment removes most contaminants, deficiencies in treatment and exposure during processing can result in the transmission of enteric and respiratory pathogens. The most at-risk populations, who are irrigating with wastewater, are: 

  • WWTP workers 
  • Sewer cleaners 
  • Farm workers 

In addition, those living close to WWTPs or irrigated crops are likely to be exposed through contaminated water supplies, aerosols, or fruits and vegetables. 

Understanding Biological Wastewater Hazards and the Possible Risks 

Untreated, or insufficiently treated, wastewater creates enormous biological risks, that put the health of wastewater workers and adjacent communities at risk: 

  • Bacterial 
  • Viral 
  • Fungal 
  • Parasitic pathogens 

Deploying a multiple-barrier system consisting of treatment, engineering controls, personal protective equipment (PPE), and community awareness is necessary to reduce illness and long-term health effects. 

Types of Biological Hazards 

  1. Bacteria

Enteric bacteria are among the most frequent hazards: 

  • Escherichia coli, Salmonella, Shigella, and Campylobacter spp. induce gastrointestinal disease manifesting such as diarrhea, fever, and cramps. 
  • Legionella spp. grows in aerosol-generating systems, which cause Legionnaires’ disease and Pontiac fever. 
  • Wound infections and respiratory illness, especially in vulnerable workers, can be caused by opportunistic pathogens like Pseudomonas and Aeromonas spp. 

  1. Viruses

Human enteric viruses that are resistant to standard treatment are frequently found in wastewater: 

  • Hepatitis A and E viruses cause acute hepatitis. 
  • Explosive gastroenteritis outbreaks are caused by Norovirus. 
  • Enteroviruses (e.g., poliovirus) are likely to circulate asymptomatically but risk inducing illness in populations of low immunity. 

  1. Parasites

Protozoa and helminths in wastewater are particularly difficult because they have low infectious doses and resilience in the environment: 

  • Giardia lamblia and Cryptosporidium parvum induce chronic diarrhea and malabsorption. 
  • Ascaris lumbricoides eggs are able to survive in the soil and infect through ingestion of contaminated produce or soil. 

  1. Fungi

Fungal spores like Aspergillus colonize organic matter in sludge and biofilms. Inhalation may cause allergic reactions, hypersensitivity pneumonitis, and asthma in long-term exposed workers. 

Occupational Hazards for Wastewater Workers 

  1. Exposure Pathways

Employees can be exposed through: 

  • Skin contact with untreated wastewater and sludge. 
  • Inhalation of bioaerosols that are produced in the course of aeration, sludge dewatering, and high-pressure cleaning. 
  • Ingestion by hand-to-mouth transfer when hygiene measures or PPE fall short. 

  1. Health Outcomes

Respiratory effects, gastrointestinal disease, and skin infections are frequently reported in WWTP workers. An endotoxin exposure of 14% of workers’ personal exposures exceeded recommended occupational exposure limits and was associated with airway inflammation in a European study. Gastrointestinal pathogens isolated in wastewater have been associated with diarrhea and enteric infection in sewage workers. 

  1. Risk Characterization and OELs

Quantitative microbial risk assessment (QMRA) models enable tolerable pathogen loads to be calculated to achieve health-based goals (e.g., DALYs). A multiple-barrier strategy for integrating treatment and control measures is advocated by the World Health Organization to ensure necessary pathogen reductions. 

Community Health Risks 

  1. Contamination of Drinking Water

Runoff from irrigated fields using untreated or partially treated wastewater can seep into groundwater and pollute wells. Surface runoff during storms carries pathogens to drinking-water supplies, leading to diarrheal disease in surrounding communities. 

  1. Aerosolization and Sprinkler Irrigation

Wastewater sprinkler application can create pathogen-contaminated aerosols. Research finds higher Seroprevalence of norovirus and Salmonella antibodies in adults who reside close to spray-irrigation fields. Furrow or flood irrigation with high fecal coliform levels (>10⁴ FC/100 mL) increases children’s infection rates who play in irrigated fields. 

  1. Foodborne Transmission

Food from produce irrigated with contaminated water represents a serious hazard. Pathogens bind onto leafy greens and can survive post-harvest treatment. Cryptosporidium oocysts and Giardia cysts are resistant to washing, which has caused outbreaks associated with salad greens. 

Control Measures 

  1. Engineering and Treatment Controls

  • Primary, secondary, and tertiary treatment: Satisfactory elimination of organic material, solids, and pathogens. UV disinfection and chlorination inactivate viruses and protozoa. 
  • Sludge treatment: Anaerobic digestion and lime stabilization kill viable pathogens in biosolids before land application. 
  • Enclosed processes: Tank covering and local exhaust ventilation prevent bioaerosol release. 

  1. Administrative and Work Practice Controls

  • Training and hygiene: Ongoing worker training on hazards, handwashing practices, and safe handling practices minimize exposure. 
  • Medical surveillance: Regular health assessments for early recognition of work-related diseases. 

  1. Personal Protective Equipment (PPE)

  • Dermal protection: Waterproof gloves, suits, and boots prevent contact with wastewater. 
  • Respiratory protection: N95 or greater-level respirators during aerosol-generating procedures. 
  • Eye and face protection: Goggles or face shields to avoid splash injury. 
  • Community-Level Interventions 
  • Buffer zones: Creating setback distances among irrigation fields and residential areas to reduce aerosol drift. 
  • Safe irrigation practices: Implementing drip irrigation or sub-surface techniques to reduce surface contact and aerosolization. 
  • Water quality monitoring: Regular testing of wells and surface waters for fecal indicator bacteria and protozoan cysts. 

Best Practices to Treat Biological Hazards in Wastewater 

To properly address biological hazards in wastewater, the following best practices can be carried out: 

  • Biological Treatment Processes: Use aerobic and anaerobic biological treatment processes to shorten the duration of organic matter degradation and reduce the risk of biohazards through biological activity. Biological treatment methods include activated sludges, trickling filters, rotating biological contactors, and anaerobic digesters. 
  • Disinfection: Disinfecting procedures, such as chlorination, UV, and ozonation, should follow biological treatment to inactivate remaining pathogens in the treatment process. 
  • Advanced Oxidation Processes: Advanced oxidation processes (AOPs) generate reactive species that may chemically degrade pathogens and resistant contaminants. AOPs increase removal efficiency better than conventional wastewater treatment. 
  • Membrane Filtration: Membrane bioreactors (MBRs) and filtration technologies (reverse osmosis and nanofiltration) are suitable for separate microorganisms and suspended solids. However, membrane fouling and cost are potential influent quality concerns. 
  • Constructed Wetlands and Natural Systems: Tertiary treatment can be completed with natural or constructed wetlands to remove pathogens and nutrients via biological uptake and environmental processes. 
  • Occupational Safety Measures: Provide wastewater treatment personnel PPE, hygiene protocols, training, and vaccination to reduce the risk of exposure to biological hazards in wastewater. 
  • Monitoring and Control: Consistently monitor microbiological indicators and treatment effectiveness, as well as sustaining the surroundings (temperature, pH, oxygen concentrations) that minimize pathogen removal during biological processes.  
  • Integrated Treatment Approaches: Integrate physical, chemical and biological treatment processes, in stages to optimize the removal of different biological hazards and newly occurring contaminants.  
  • Waste Sludge Management: Treat and dispose of biosolids in a manner that avoids secondary biohazard risks (e.g., pathogen resurgence and environmental contamination). 

 

Conclusion 

Biological contamination in wastewater presents an imminent risk to employees and adjacent populations through a multitude of exposure pathways. A comprehensive approach, considering wastewater reuse, is necessary to mitigate health risk through: 

  • Innovative treatment 
  • Engineering controls 
  • Work practices 
  • PPE 
  • Community protection 

Ongoing monitoring, risk assessment and implementation of WHO health-based targets will sustain pathogen load within acceptable ranges and avoid enteric, respiratory, and dermal outbreaks.