Here are a few problem-solving and time-saving devices which we constructed very inexpensively for use in our laboratory and sampling activities.

BOD bottle rinser

Activated sludge stirrer

Rag-free sewer sampling

BOD bottle rinser:

Many labs have problems with excessive D.O. depletion in the dilution water control bottles. Although the quality is of the water used to make up the dilution water is often the cause, poor washing or rinsing technique can also be an important factor. Most detergents in use today are biodegradable, and that means BOD! So, thorough rinsing is critical. We devised a ten-bottle rinser which is pictured here, taken apart, and below, in use.

The base was sized by placing ten bottles on a piece of paper and drawing around them, leaving room for a divider running the long way. A cover was designed to fit over the base with the bottles in it, so that it could be inverted for draining. The holder was constructed to our specifications by the local high school metal shop out of open aluminum sheeting-- which we actually got at a scrap yard. The water "distributor" was made by our WWTP machine shop from copper tubing. It consists of a rectangular "ring" of 1/2 inch (12.7mm)(inside diameter) tubing with a cross piece into which is inserted an inlet of 1/4 inch (6.35mm) i.d. tubing. Ten lengths of 1/4 inch tubing protrude downward from the ring at the appropriate spacing to fit into the bottles. I don't have the original plans, but the best way to make sure everything fits is to design it around an actual set of bottles in order to get the proper dimensions.

After brush-scrubbing each bottle with detergent and water, we place the bottles into the base, where they fit tightly. The base is placed on a "milk case" in the sink. The distributor ring is rested on top of the bottles, being sure to fit the individual wash tubes into the mouth of each bottle. (This part can be a little difficult with stiffly soldered connections between the tubes and the ring, and we are currently holding some of them in with duct tape, which is working nicely.) If you have fewer than ten bottles, you can place small rubber eye-dropper bulbs over the ends of the unused tubes. A heavy rubber hose attached to a lab faucet fixture is connected to the inlet tube and held in place with a hose clamp. (The fixture needs to be the type with a vacuum breaker for cross-connection prevention)
The water is run for ten minutes to rinse the bottles thoroughly. Then the water distributor is taken out of the bottles, the cover is put over them, and the unit is inverted for draining. It is then set right-side up; the cover is removed, some distilled water is squirted into each bottle, the cover is replaced, and the unit is inverted to drain again. This sequence of distilled-water rinsing is repeated two more times, after which the bottles are removed and placed upside-down in another milk case to dry. (Note: The bottles dry quicker if the milk case is tipped at a small angle so that a persistent hanging drop does not form in the center of the bottle.) We originally had hoped to do the distilled water rinses using the distributor,as well, but there was not enough pressure to spread the water evenly to all the bottles.
We have been rinsing our BOD bottles with this device for 15 years now and find that it is very thorough and efficient.

Activated sludge stirrer:

In order to get accurate and reproducible settling data, it is important not to shake the sludge too hard before pouring it into the settleometer. We found that people of different size and strength may have different ideas of what is meant by the word "gentle". [We had noticed that our weekly-average graph of sludge volume index (SVI) showed a distinctive, regular, saw-tooth pattern. At that time, we had two lab technicians, a 4'10" woman and a ~ 6' man, who alternated weekly in making the sludge measurements. .]
. We tried to devise a simple, manual stirrer that would could be used to mix the sludge in the sample bottle before pouring, in the hope that it would eliminate the differences in shaking. It was sized to fit into the mouth of the sample bottles we use: one-gallon, wide-mouth polyethylene bottles with molded hand grips. The diameter turned out to be about 3.25 inches. We made it from a soft polyethylene jar cover, such as is used on quart tubs of "Marshmallow Fluff^®" . Rounded triangular holes were cut into it so that it could be raised and lowered easily in the liquid. Tabs were bent up and down along the outside edge to improve mixing. The tabs can be made to stay in place by placing the disk in boiling hot water and cooling while the holding the tabs in the bent position (not with your fingers). The disk is held in place by cutting a groove in a piece of dowel, making a hole in the center of the disk which is smaller than the dowel's diameter, and sliding the disk up into the groove. The stirrer, which we refer to as the "ski pole", because of its appearance, is placed into the mouth of the bottle and moved up and down while twirling it in the fingers. We found that, even though there may be some difference in the intensity with which different people mix with this stirrer, it was apparently had much less effect on sludge breakup than the differences which occurred when people mixed the sludge by "gently" shaking the bottle.
The picture shows the sample bottle and a settleometer, with the stirrer lying across them. The stirrer has been in use for about 15 years, also, with no need of repair in that time. Since we always use two or three settleometers at once, we also use the stirrer to re-mix all of them gently just before starting the timer.
One more thing you may notice in the picture is the jacket around the settleometer. We found that when the room temperature is significantly higher than that of the sludge sample, the effect of gas formation may slow the compaction-- the phenomenon that eventually causes the sludge to rise. The "winter jacket", cut from a styrofoam acid-bottle shipping container, helps to slow this process by insulating the settleometer to keep the sludge from warming as fast.

Rag-free sewer sampling:

There is a meter house at the boundary of a neighboring town whose wastewater flows into our collection system for treatment at our plant. The flow is measured by the depth of the wastewater in a flume-like section of pipe, which is, I believe, a "Kennison nozzle." Formerly, the depth was measured by a float arm; a few years ago, that was replaced by an ultrasonic meter. The flow data are telemetered to our treatment plant.
Our contract with the town requires 24-hour composite sampling twice a month at the meter house for BOD and TSS analysis. Use of a weighted strainer on our sampler hose caused problems because of "rags" and other debris getting caught on it. Without the strainer, however, the end of the tubing would float out of the water and sample mostly air. Charles Goddard, who worked in our lab at that time, designed the floating sample hose holder depicted below.
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The device is made mostly from 1/2" (12.7mm) i.d. 5/8" (15.9mm) o.d. rigid PVC tubing. A 3/4" (19.05mm) PVC "tee" is cemented onto one end. A top part of the tee has had a slot cut into it the long way so that it forms a hook. A hole is cut into the main tube about 1/5 of the way down from the tee for inserting the sampler tubing. The original design calls for making this section of the tube wider using two 3/4"-to-1/2" adapters connected together by a short piece of 3/4" tubing to make the insertion of the sampler hose easier. This might not be necessary if the hole is drilled in at an angle, but it certainly serves to strengthen this part of the tube. (There was also a tip of semi-rigid polyethylene tubing inserted in the end of the PVC tube. When this got "lost" in the flow, we found that it works fine without it.) The whole device is about two feet (60 cm) long, but the length should probably be designed to fit the particular location where it is to be used.

The first drawing, by Mr. Goddard, shows how the holder is used in the sewer. A piece of rigid 1/2" PVC tubing is attached across the open pipe; this part can be left there permanently. It is important to locate this far enough downstream of the level measuring apparatus so as not to interfere with the readings. The hose from the sampler is threaded into the hole which is located part way down the holder tube and pushed through so that it protrudes from the end. We then use a pole with a hook on the end to lower the holder into the sewer and hook the slotted tee over the tubing which lies across the pipe. We have not had to go down there except initially to set up the cross-tubing. The end of the holder is kept partially supported by the flowing water. (The polyethylene tip may have been intended to help the end float higher, because of its low density.) The slotted tee swivels like a hinge on the cross-tube as the water level changes, so that the end stays at about the same depth. Nothing has ever gotten stuck on this holder in the many years we have been using it. Any rags or paper which come along simply lift the end of the holder and pass by. This device has been a great solution to the problem.

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Safety and Health Tip: In addition to wearing gloves and safety glasses at all times in the lab, here is a very important tip I would like to pass along:

Keep your mouth closed when you are pouring samples. They splash!  

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