The microscale flocculation test (MFT)—A high-throughput technique for optimizing separation performance

• The conventional jar test was scaled down into a 12-well microplate format.
• Tumble stirrer mixing speed was characterized through video motion tracking.
• The dose-dependent dewatering profile was a strong function of the flocculant type.
• Multi-stage dosing and digestate source can significantly affect dewatering results.
• Our high-throughput approach is ideal for optimizing the flocculant type and dosage.

In this work, a new microscale flocculation test (MFT) method was developed that is ideally-suited for optimizing separation performance. A critical and complicated task in wastewater treatment is to identify the flocculation conditions that yield the optimal separation of water from suspended solid materials. The standard ‘jar test’ method is inadequate for conducting a full process optimization because a typical set-up only allows for a maximum of 6 tests to be conducted at once and fairly large volumes of materials (approximately 1 to 2 L) are needed for each individual test. The microplate-based, parallel processing format of the MFT method allows for dozens of flocculation tests to be conducted simultaneously, with each test requiring only a few millilitres of material. As a demonstration of the MFT method, ten cationic polymer flocculants were evaluated with various digestate types. The optimal separation performance, as determined by the lowest capillary suction time (CST), was found by rigorously evaluating the effect of flocculant type (including molecular weight and charge density) and dosage conditions (including total amount added and single versus staged addition). For example, the dose-dependent profiles for certain flocculants exhibited a nearly 10-fold greater decrease in CST compared to other flocculants. Process optimization in environmental separations is not trivial, but rather, is a complicated task that requires an extensive amount of experimental work for which the MFT method is ideally suited.

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