Sludge dewatering: presses and geotextile bags

Description

Dewatering of sludge by belt press, screw press or geotextile bags, on one mass balance. A fraction of the solids, the capture, leaves in the cake at the cake dryness; the rest returns to the plant with the filtrate.

$M_t = M_s \cdot captura \qquad M_{torta} = \frac{M_t}{ST_t}$

$Q_f = Q_l + Q_{pol} + Q_{lav} - \frac{M_{torta}}{\rho} \qquad SS_f = \frac{M_s - M_t}{Q_f}$

Polymer consumption from the dose per tonne of dry solids, and its dosing flow at the solution concentration. Presses and feed pumps run part of the week, so the hourly loads are the weekly solids concentrated into the operating hours:

$M_{s,op} = \frac{7 \, M_s}{D \, H}$

Belt press. Belt width for the larger of the solids loading (kg/(m.h)) and the hydraulic loading (m³/(m.h)), rounded up to whole presses, plus the belt wash water returned with the filtrate. A thin feed is governed by the hydraulic load; thickening upstream shrinks the press.

Screw press. Units for the larger of the solids and hydraulic capacity per unit.

Geotextile bags. Dry solids per bag from its volume and the dryness at the end of filling, fill time, bags per year, bags on the pad while filling and drying, pad area, and the mass for disposal at the dryness reached after drying:

$M_{bag} = V_{bag} \, \rho_t \, ST_t \qquad t_{ench} = \frac{M_{bag}}{M_t} \qquad N_{patio} = \left\lceil \frac{t_{ench} + t_{sec}}{t_{ench}} \right\rceil$

Typical values, to be confirmed with the manufacturer and tests on the sludge (undigested excess activated sludge sits at the low end):

References

ANDREOLI, C. V.; VON SPERLING, M.; FERNANDES, F. Sludge Treatment and Disposal. Biological Wastewater Treatment, v. 6. IWA Publishing, 2007.

METCALF & EDDY. Wastewater Engineering: Treatment and Resource Recovery. 5th ed. McGraw-Hill, 2014.