Wastewater Lab: Safety & Chemical Storage

• General safety practices in a wastewater laboratory relate to food and beverages, chemical storage, acid dilution, MSDS, venting of equipment, and chemical storage.

Chemical Storage

• Chemicals should be stored in a cool, dry, and dark location, preferably in a cabinet.
• Liquid chemicals should be stored below face level.
• Chemicals must be dated upon receipt with expiration dates recorded.
• Acids should be stored separately from other chemicals and below eye level.
• Always check the chemical label for hazard and storage information.
• Keep Material Safety Data Sheets (MSDS) available for review.
• Chemicals should never be stored in unmarked containers.
• All prepared reagents should be labeled.

Sampling

• A Grab sample represents a single instant.
• A Composite sample represents a longer time period and averages water quality.
• A WPDES Permit specifies sample location, type, frequency, and parameters to be tested.
• Grab samples should be collected in well-mixed areas, in the center of the waste stream, off the channel floor, and in a clean flow channel.
• Grab samples are for instantaneous measures of pH, chlorine residual, dissolved oxygen, fecal coliform, oil and grease, volatile organics, and cyanide.
• Flow Proportional Composite Sampling is representative and calculates loading rates of BOD, suspended solids, phosphorus, and ammonia.
• Automatic Samplers pull aliquots proportional to flow with programmed volume and intervals.
• Composite Autosamplers collect into large jugs and may require sub-sampling with mixing.
• Split Samples are divided for analysis to assess variability, precision, and discharge permit compliance.
• Sample Documentation includes sample type, point, ID, time/date, preservation, sampler initials, and observations.
• The Sample Collection Date is the majority collection date used for DMR.
• Volumetric Flasks are used for sample collection with proper documentation and preservation.

Equipment

• Volumetric Flasks are for making standards, especially for calibration.
• Beakers & Erlenmeyer Flasks are for digestion, not standard preparation or volumetric measurements.
• Graduated Cylinders are for BOD & TSS with 50 mL or more of sample.

Pipets

• Volumetric (micro-bore) pipets are for standard preparation.
• Wide-bore pipets are for BOD & TSS samples.
• Mohr pipets are for color reagent (phosphorus).
• Serological (wide bore) pipets are for BOD influents (low volume) and preservation of phosphorus or ammonia samples.
• Mohr Pipets graduations stop before the tip.
• Serological Pipets graduations continue to the tip with blow out or drain out options.
• Volumetric Pipets are classified as "TD" (To Deliver) and should not be blown out.
• Use wide-bore pipets for samples with particulates.
• Pipet accuracy decreases as volume decreases; larger pipets are more accurate.
• Incubators maintain constant temperature for microbial or chemical analyses.
• Desiccators maintain a humidity-free environment and must have indicating desiccant and proper sealing.

Balances

• Analytical Balances have high sensitivity (0.1 mg) for TSS testing.
• Top-Loading Balances measure 150-300 g but are less accurate.
• Balances should be verified monthly, ensuring they are level and clean, and avoid drafts; use weigh boats for chemicals.
• Weights should be stored properly and handled with care, cleaned with soft brushes, and re-certified every 5 years; use ASTM Type 1 weights for analytical balances.
• Drying Ovens should maintain temperature, avoid overloading, and ensure proper sealing.

Reagent Water

• Reagent Water is treated to remove impurities affecting sample analysis and is classified as ASTM Type I or Type II.
• Use Teflon, glass, polyethylene, polycarbonate, or polypropylene for storage; avoid long-term storage after opening; discard if cloudy or quality changes.
• Conductivity measures water quality; pure water has low conductivity; presence of ions indicates impurities.
• High Conductivity indicates dissolved ions affecting test results.
• Heavy Metals are toxic and can inhibit biological tests.
• Dissolved Organics from carbon filtration failure may interfere with tests.
• Standards are known concentration solutions used for reference.
• The Calibration Curve requires accurate measuring devices; standards should be prepared in similar solutions to samples; read meniscus at eye level.

BOD Testing

• Maintain an initial DO close to saturation (8.2-8.5 mg/L).
• Incubate samples for 5 days in the dark at 20 ± 1°C.
• A minimum of 2 dilutions is required; 3 are recommended, and 5 dilutions for unfamiliar samples.
• The minimum volume for BOD without dilution is 3 mL.
• BOD Calculation Formula: BOD (mg/L) = [(iDO - fDO) - SCF] × DF
• Use seed correction factors for GGA.
• Decreased BOD with increased sample volume may indicate toxicity.
• LCS are required for accuracy weekly or after 20 samples with acceptance criteria for LCS: 198 ± 30.5 mg/L.
• High bias causes: nitrification, cold GGA, contamination.
• Low bias causes: insufficient seed, weak seed materials, old GGA.

TSS Testing

• Total Suspended Solids (TSS), also known as Non-Filterable Residue (NFR), measures water quality in wastewater treatment.
• It is measured by filtering a water sample through a pre-weighed filter, drying, and weighing again.
• Composition is ~70% organic, ~30% inorganic.
• TSS measures wastewater strength, process efficiency, and loadings.
• Reducing TSS improves disinfection and compliance with standards.

Drying Oven

• Maintain at 103-105°C (104 ± 1°C) with proper ventilation.
• Check oven temperature daily.

Filter Type

• Use glass fiber filters without organic binders and pre-rinse filters.

Weight Measurement

• Initial weight is recorded after drying to constant weight.
• Constant weight is defined as no change in weight.