Run protocol

Stock, 5 litres. Enough for a calibration series and three column charges.

Stir again immediately before drawing every sample. Solids settle in minutes, and settled stock reads as clean water.

Laboratory sieves give the cleanest result but are not required. Whatever the method, report it plainly and give numbers actually measured rather than a nominal mesh size.

Sedimentation needs no equipment at all: crush the scoria, shake it in a tall bottle of water and let it settle. Coarse grains reach the bottom first and fines last, so decanting at timed intervals separates the fractions. It is settling-velocity separation, the same principle as the hydrometer analysis used in soil mechanics.

Lump charcoal, never briquettes: briquettes carry binders that leach into the water. Pieces should look like broken black wood, not uniform pillows.

1. 01

   Crush it with pressure, not blows

   Inside two nested bags, stand on a board laid over it or roll a glass bottle across it.

2. 02

   Keep what stays on the mesh

   The powder that falls through would wash out and turn the effluent black.

3. 03

   Rinse until the water runs faintly grey

   Change the water in the bucket as many times as it takes.

4. 04

   Soak overnight until it sinks

   Dry charcoal is full of air and floats up through the layer above it. Simmering it in water for 15 minutes does the same job faster.

The checker target and white reference card for the photometric rig, at true size on one A4 page. Print at 100% and check the 100 mm scale bar with a ruler before cutting.

Download target sheet (PDF)

Or generate it with rwl target.

Five levels, 200 ml each.

Photograph each in the same jar, washing and drying it between levels.

1. 01

   Photograph the influent

   Stir the stock, fill the jar, shoot it as influent.

2. 02

   Charge the column

   Close the valve and pour 884 ml of stock in at the top.

3. 03

   Open the valve and start the timer

   Collect the effluent in the measuring jug.

4. 04

   Record the flow rate

   Time how long 500 ml takes to pass.

5. 05

   Photograph the effluent

   Same jar, same fill level, same position. Name it charge1, then charge2 and so on.

6. 06

   Repeat, at least three charges

   The first charge reads best and removal drops as the bed loads. That curve is the useful result, not the single first number. rwl report --before influent --after charge1 charge2 charge3 prints it as one row per charge.

Timing the first charge is a falling-head permeability test: the column is its own standpipe. Measure once how far the hose outlet sits below the base of the bed, run the charge with the valve fully open, then:

rwl permeability --seconds 45 --outlet-drop 0.30

It prints the bed's hydraulic conductivity, the same bed at 0.37 g, and how long 500 ml should take at slow sand filtration rates. If the column runs faster, throttle the valve for the measured runs. For a full drainage curve, film a cork float with a skewer against a ruler and pass the levels with --series level.csv.

• Depth and volume of each medium as placed, and the graded yield from the raw scoria
• The grading method and its measured aperture or settling times
• The greywater recipe actually used, not the one planned
• Flow rate and removal percentage per charge
• Room temperature

Photograph the build at every stage, including the versions that did not work, the graded fractions side by side, the five calibration jars as a gradient, and influent next to effluent.