The continuous activated sludge process has been successfully employed in public health engineering installations for nearly a century. The Armfield Aerobic Digester is a benchtop unit designed as a comprehensive study facility of this process.

A synthetic waste water feed may be used to gain a working knowledge of the operational parameters and purification efficiencies.

Description

Waste water is drawn from a floor-standing feed tank (not supplied) by a DC motor-driven peristaltic pump. Rotational speed – and thus flow rate – is accurately set by a ten-turn potentiometer.

The pump delivers the feed to the reactor vessel through a transparent lid. Air is supplied at a measured rate by a small compressor, and discharges into the base of the reactor via a spider-arm dispenser. This design prevents blockages and produces sufficient bubbling for stirring and reaction. The liquid level in the reactor is maintained at a constant value of five to ten litres, by an adjustable overflow device connected to the outer annular chamber of the vessel. Discharge is by gravity to a floor-standing product tank (not supplied).

The reactor temperature is maintained by a three-term controller, which varies power to an immersion heater within the vessel. Any temperature between ambient and +35°C may be selected, the best conditions being a few degrees above the diurnal maximum in the user’s laboratory.

Dissolved oxygen and pH probes and meters are included.

The reactor lid contains a gas exit port, suitable for sampling the gases for subsequent analysis.

Features & Benefits

• Small Scales bench mounted design
• Provides demonstration of continuous activated sludge process

Demonstration Capabilities

• Acclimation of a completely mixed biological reactor
• Measurement of COD and MLSS changes as criteria of performance
• Establishing the stoichiometry and kinetics of aerobic processes
• Gas/liquid mass transfer
• Residence time distributions
• 100% scale-up to industrial requirements
• Studying the effect on effluent quality of:
  • Inflow substrate concentration (‘loading rate’)
  • Liquid flow rate and reactor volume (‘detention time’)
  • Air flow rate
  • Temperature
  • pH stability
  • Nutrient deficiency

Technical Specifications

Feed pump: 24V DC, peristaltic, 0-30rpm corresponding to 0-40 L/day
Air compressor: 120V/240V, 0-3.0 L/min (STP)
Reactor vessel: 10L maximum capacity
pH meter range: 0.00 to 14.00
DO meter range: 0-100% saturation, resolution: 2%
Reactor heater: Toughened glass, electrical immersion 200W
Temperature controller: 3-term PID (temperature limit set at 35°C)

Length: 1.00m
Width: 0.50m
Height: 0.50m

Requirements

Electrical supply:

W11-A: 220-240V/1ph/50Hz

W11-B: 120V/1ph/60Hz

W11-G: 220-240V/1ph/60Hz

Plastic feed and product tanks – capacity typically 30-50l, floor standing (not supplied)

Synthetic waste water (not supplied)