No statement contained in this chapter shall be construed as preventing any special agreement or arrangement between the city and an industrial concern, whereby an industrial waste of unusual strength or character may be accepted by the city for treatment, subject to payment therefor by the industrial concern, provided such payment shall be consistent with the user cost system in requiring the industrial concern to pay its proportionate share of costs to the utility arising from the acceptance of such industrial waste.
(‘85 Code, § 9.05(k))