Define the question and the sampling location
Characterising a discharge is different from characterising the actual feed to a UF plant. Sample after the operations that will remain in the proposed process and document whether equalisation is working. A bottle taken from a settled corner of a tank may represent the tank bottom rather than the water entering the feed pump.
Prepare a schedule covering products, shifts, CIP operations and low-production days. Record flow, time and process conditions. Keep a concentrated cleaning discharge separate from the blended feed when studying its effect. Creating an arbitrary mixture of convenient samples can hide the operating condition that the plant must handle.
Choose grab samples, composites or both
A grab sample describes a particular moment or a homogeneous batch. It helps investigate extremes and properties that change during storage. A composite combines aliquots across the relevant period. When flow varies significantly, weighting by discharged volume avoids assigning the same importance to a small purge and a large process discharge.
Illustrative calculation: 10 m³ at 200 mg/L followed by 30 m³ at 600 mg/L produces a flow-weighted average of 500 mg/L. Averaging the two concentrations without weighting gives 400 mg/L and understates the load. Neither average, by itself, describes the 600 mg/L maximum that the equipment may receive.
Separate preserved analysis samples from test feed
Ask the laboratory to specify parameters, containers, volumes, preservatives and holding times for each method. An acid-preserved bottle intended for particular chemical analyses is not automatically suitable for filtration or biodegradability testing. Reserve suitable unaltered feed when the treatment trial requires it and agree transport and prompt use.
Label bottles and retain custody records, receipt temperature and sampling and analysis times. Do not prefilter the feed sample unless that filtration belongs to the proposed treatment train. Preservation can alter emulsions, aggregates and biological activity even when it allows a particular analytical measurement to remain valid.
Turn the results into a design range
Provide the complete analytical set together with the production schedule, including explanations for unusual results. Distinguish routine feed, reasonably foreseeable peaks and events that will be diverted or stored. That distinction helps establish which conditions require a pilot and which problems should be corrected upstream of the membranes.
Common questions
Does a composite sample replace grab samples?
No. It can represent average loading while concealing a short discharge that is incompatible with the equipment. Retain grabs for critical events and field measurements for unstable properties.
Can one container serve every analysis and trial?
Only when the laboratory confirms its suitability. Chemical preservation, headspace, container material and required volume may conflict between analytical parameters and treatment tests.