Water, hygiene, sanitation and microbial control
Move from water recycling alone to complete management of sanitary quality, uses, liquid waste and microbial contamination.
Mastery objectives
- identify the functions, interfaces and degraded scenarios specific to the subject
- repeat simple calculations and verify units, assumptions and margins
- turn a principle into a verifiable procedure or decision
- connect the subsystem to human, energy and logistics constraints
1. Recovered water is not automatically potable water
A loop can recover a large fraction of water while salts, organic compounds or microorganisms remain. The sanitary chain combines separation, filtration, chemical or catalytic treatment, disinfection and monitoring. Success is not only mass efficiency: water must meet the specification of the use for which it is released.
2. Separate water qualities reduce unnecessary treatment energy
Not every function needs the same water quality. Drinking and food preparation require the strictest control, while technical cleaning, rinsing or some industrial processes may accept a different grade. Clearly separated networks avoid over-treating every liter, provided cross-connections and backflow are prevented.
3. Microbiology: prevent biofilm from becoming a system failure
Pipes, tanks and wet surfaces can support microbial communities and biofilms. Biofilm can degrade water quality, bias sensors and increase pressure drop. Control combines compatible materials, circulation, disinfection, sampling and the ability to clean or replace affected sections.
4. Human hygiene is a health problem and a water-budget problem
Washing, toilets and clothing create large flows with different contaminants. Procedures must limit consumption without degrading skin health, sleep or infection prevention. Hygiene therefore connects medicine, psychology and water-loop sizing.
5. Sanitation and liquid waste streams
Urine, graywater, condensate and laboratory effluent should not be mixed without considering how each contaminates the recovery process. Every stream is characterized before choosing recovery, separate treatment, storage or controlled disposal. Laboratory chemicals may make a stream incompatible with biological processing.
6. Quality control: measure enough to make a decision
Conductivity, organic carbon, pH, disinfectant residual and microbiological assays answer different questions. A settlement defines frequency, thresholds, confirmation methods and the response when sensors disagree. An out-of-limit value must lead to quarantine or reprocessing decisions rather than becoming only a logged alarm.
7. Sanitary barriers: prevent contamination from flowing back
A crewed water network is not only a sequence of filters. Taps, showers, laboratories, crop systems and maintenance equipment can drive contaminants upstream if pressure relationships or check valves are poorly controlled. Design therefore needs backflow barriers, separation between clean and technical uses, and explicit rules for where treated water may re-enter circulation. Water can be chemically acceptable and still become microbiologically problematic when biofilms establish in piping. Monitoring should combine online measurements with sampling and clear criteria for isolating a suspect volume.
8. Sanitation: close loops without mixing every hazard
Greywater, urine, solid waste and laboratory effluent do not share the same composition or risk. Mixing them too early can complicate treatment and make failures harder to diagnose. A settlement can preserve distinct streams until an appropriate process transforms them, which can also improve nutrient recovery. Sanitation must be coupled to energy: distillation, oxidation and heating consume power and reject heat. Degraded mode should define the minimum water quality needed for drinking, cooking, hygiene, medical cleaning and crop protection.
9. Microbiological event: isolate, sample and correct the cause
When abnormal microbial growth is detected, simply increasing disinfectant concentration is not enough. Operators need to map affected branches, check temperatures and stagnation, find the failed barrier and preserve samples before cleaning. An aggressive intervention can hide the cause while damaging membranes, seals or sensors. Return to service then requires flushing, chemical checks, microbiological analysis and enhanced monitoring. The event should produce a lasting correction such as removing a stagnation zone, changing recirculation frequency, replacing a material or improving sampling.
10. Worked example: makeup water at 98% recovery
If six people together produce 30 L/day of recoverable water and 98% is actually recovered, nominal loss is 30×0.02 = 0.60 L/day. Over 500 days the makeup requirement is already 300 L. At 95% recovery the loss becomes 1.5 L/day, or 750 L over the same period. Three percentage points therefore add 450 L of logistics in this example.
11. Exercise
Draw a system separating potable water, technical water, graywater and urine. Inject microbial contamination into one tank and describe isolation, sampling, treatment, return to service and medical communication.
12. Reasoned solution
Separate the suspect tank from the potable network, preserve a verified reserve for vital use, sample before disinfection, then test upstream and downstream branches to locate the failed barrier. Return to service is justified only after treatment, flushing and results confirm the defined acceptance criteria.
13. Validation mini-project
Design the sanitary plan for a twelve-person habitat: water balances, quality by use, microbial surveillance, cleaning, special effluent, emergency reserves and an out-of-specification water procedure.