Program Control Commands

MEN -- Causes a list of available commands to be typed. In the graphics version, requires a carriage return to be typed before entering any more commands.

SIM -- Allows the user to run the simulation for periods of hours and minutes.

DAY -- Allows the user to run the simulation for periods of days and hours.

TRE -- Used to produce a display of trended variables.

INI -- Used to initialize the four variables that will be trended.

END -- Ends trending and wipes out all stored data.

SAV -- Saves the current situation for future restoring.

RES -- Restores simulation to the most recently saved condition.

DES -- Design a new system, wiping out the current one.

INF -- Enable or disable use of input file.

OUT -- Enable or disable generation of output file.

STO -- Stop ESIM and return to DOS.

Process Control Variables

RET -- Change the return rate.

WAS -- Change the waste rate.

FEE -- Change the fraction of the feed entering each pass (in step-feed only).

FLO -- Change the average flow, but the flow continues to vary with the hour of the day.

FLS -- Set the flow to a constant, independent of time of day.

FLD -- Set hourly influent flow rates, in MGD.

BOD -- Change the influent biochemical oxygen demand.

KLA -- Change the aeration rate. The KLA is proportional to the amount of air, so doubling the KLA is equivalent to doubling the volume of air (7.0 per hour)

SVI -- Change the sludge volume index. An SVI less than 160 slows down the simulation.

EFF -- Proportionality factor for effluent suspended solids (15).

Model coefficients

Y1-- Changes yield coefficient for the conversion of stored to active mass (0.66).

Y2-- Yield coefficient for conversion of active mass to inert mass (0.25).

OXS -- The saturation value for dissolved oxygen (69 lbs./million gallons).

KDO -- Monod constant for oxygen utilization (8.0 lbs/MG).

RT -- Rate constant for conversion of S to XS (3 per hour).

RXA -- Rate constant for conversion of XS to XA (0.2 per hour).

RXI -- Rate constant for conversion of XA to XI (0.00125 per hr).

CF -- Correction factor for oxygen uptake rate (24).

KS -- Monod coefficient for substrate uptake (1250 lbs/MG).

KXS -- Monod coefficient for conversion of XS to XA (150 lbs/MG).

FH -- Maximum ratio of XS to XT (0.45).


SCH -- Produces schematic display.

BAR -- Produces bar-graph display.

NUM -- Produces numerical display.

MRK -- Places a mark on time scale of trend display.

PRN -- Print the display.

TBL -- Print a table of trended results.


BOD -- Influent biochemical oxygen demand (mg/l).

FLO -- Influent flow (MGD).

RET -- Return flow (MGD).

WAS -- Waste flow (MGD).

MLSS - Mixed liquor suspended solids (mg/l).

RAS -- Return activated sludge suspended solids (mg/l).

ESS -- Effluent suspended solids (mg/l).

EBOD - Effluent biochemical oxygen demand (mg/l).

KLA -- Aeration rate constant (per hour).

SLR -- Solids loading rate on the clarifier (lbs/day/sq ft).

MASS - Total pounds of biomass in the system (lbs).

SVI -- Sludge volume index (ml/g).

AVDO - Avg dissolved oxygen concentration in the aerator (mg/l).

WLD -- Waste load, pounds per hour wasted (lbs/hr).