Instead, foaming was caused by ferric chloride reacting with biodegradable surfactants in the influent. Testing revealed that after wastewater solids had been removed in the ballasted flocculation basin, surfactants had nothing to attach to, and once flow discharged over any weir or rock structure that induced turbulence, the surfactants began to foam.
..... In an attempt to quantify the surfactants in the plant’s influent, samples were sent out for anionic surfactant tests. Raw influent, excess-flow storage basin effluent, ballasted flocculation basin influent (after ferric chloride addition), and ballasted flocculation basin effluent were tested.
.....Results indicated that anionic surfactant levels at all locations were very low, under 3 mg/L (normal levels for wastewater are 1 to 20 mg/L; see Table 3, above). Unfortunately, the results did not provide any more infor- mation, for several reasons. First, the surfactants my not be anionic. Second, if several surfactants are present, anionic surf actant tests will be inaccurate because of interference from other surfactants. Third, city staff did not know any industry that could be discharging a high level of surfactants to the treatment plant, making it impossible to identify the surfactants’ source.

Hunting for Solutions
.....To alleviate the ballasted flocculation foaming problems, two treatment alternatives were developed — using alter native coagulants at various doses and adding defoaming agents to ballasted flocculation basin effluent. Unfortunately, testing with different coagulants (including ferric sulfate, aluminum sulfate, and polyaluminum chlorohydrate) at varied doses resulted in significant foaming.
.....Testing with defoaming agents proved more successful. Initial jar tests used a defoamer (Drewplus A-8274) and common vegetable oil (soybean). Both the defoamer and the vegetable oil controlled foam immediately. Sodium hypochlorite was added to ensure that foaming would not occur after disinfection. Samples with and without the defoaming agent were tested for BOD to show the effect of the agent. Initial tests indicated that the agent did not affect BOD limits.

..... So, the project team checked the plant’s effluent
discharge to the Kansas River, because it discharges through a 180-cm (72-in.) pipe and flows down over a rock structure, which provides turbulence, before discharging to the river. During low flows, the elevation from the pipe to the river is 6 m (20 ft). During testing, an expanse of white foam about 15 m wide x 3 km long (50 ft wide x 2 mi long) developed as a result of the turbulence and fall. Currently, the plant’s NPDES permit prevents effluent from being discharged to the Kansas River if more than a trace of foam is visible, so the test had to be stopped until no foam was present.
.....To resolve the foaming issue, the project team reviewed both the ferric chloride and polymer doses and the primary basin effluent characteristics. The team was concerned that the polymer dose was too high, the primary basin effluent was septic, or both. The team also did jar tests on primary basin effluent to determine the optimum doses of polymer and ferric chloride.
..... Jar testing (with shaking) was conducted at various ferric dosages on storage basin effluent and on raw waste water. Raw wastewater was also tested without any chemical because of concerns about the excess-flow storage basin’s septicity because it had not been cleaned out in more than a month. During tests, foaming was seen with both raw wastewater and primary basin effluent with ferric chloride. With respect to overall solids removal performance, raw wastewater had better results than primary basin effluent.
..... The project team determined that the polymer dose was not excessive (in fact, testing established that the optimum ferric chloride dosage for good solids removal was about 90 mg/L).