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Evaporation Processes
Chapter · November 2007
DOI: 10
...

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Wang, Nazih K
...
Sakellaropoulos
CONTENTS
INTRODUCTION
SLUDGE EVAPORATION LAGOONS (SLUDGE DRYING LAGOONS)
EVAPORATORS
DESIGN EXAMPLES
NOMENCLATURE
REFERENCES
APPENDIX
1
...
1
...
The purpose is to concentrate, separate, dispose,
or utilize wastes and pollutants and to regenerate and return clean water to the environment
...

Although sand bed dewatering of sludge has been popular in small communities, heat
drying or evaporation have proved feasible in many instances
...

They become feasible when the dried sludge can be sold as a fertilizer or used as a
vitamin- and protein-enriched animal feedstock
...
Sludge return to the environment in a dry form and
utilization of its nutrient content may be ecologically more attractive than the current
trend toward incineration
...

Recent incineration practice usually involves prior removal of excess water and
sludge thickening through dewatering and drying steps
...

Furthermore, incineration equipment is often designed so as to permit flexibility of
operation during either drying or combustion
...
K
...
-T
...
K
...
, Totowa, NJ

549

550

Lawrence K
...


in various sludge and wastewater treatment designs, the associated energy demands and
costs, and the possible improvement of the market for dried sludge warrant analysis and
further evaluation of drying and evaporation
...

All involve water removal to some extent, and also reduction of the weight and volume
of the fluid sludge to that of a concentrated sludge or a moist solid
...
However, sand beds
used for physical dewatering are called “sludge drying beds,” despite the considerable
water content of the remaining cake, in order to distinguish them from other mechanical
dewatering systems
...
Drying to low water content requires high-temperature water
removal in mechanical dryers
...

The origin of the effluent stream, the final desirable moisture content, and the end use
of the sludge determine whether dewatering is sufficient, or heat drying is necessary
...

Before attempting any theoretical analysis of drying and evaporation processes, the
design and operating characteristics of some basic units will be presented
...
Drying and evaporation consist of a combination of mass and heat transfer processes common to all
dryer designs for a given sludge
...
2
...

Evaporation can be defined as the process by which liquid water is converted into a
gaseous state
...
It also requires that
the humidity of the atmosphere be less than the evaporating surface (at 100% relative
humidity there is no more evaporation)
...
For example, the evaporation of 1 g of water at a temperature of 100°C
requires 540 calories of heat energy (600 calories at 0°C) (43)
...
Comparison of drying
periods, land requirements, and solids loading rates between sand beds and lagoons obviously favor the dewatering technique
...
Precipitation and evaporation rates are the controlling factors (6,7)
...
Most
organic industrial sludges are often dried in lagoons since offensive odors are minimal
...

The theory, principles, and design of thermal evaporation process reactors are well
established and they are presented in Section 3
...
1
...


2
...
1
...
1
...
General Process Description
The sludge evaporation lagoon (Fig
...
Individual lagoons may be considered an alternate means of wastewater disposal on individual pieces of property
...

Generally if the annual evaporation rate exceeds the annual precipitation, this method
of disposal may at least be considered
...
It should be noted that for unlined on-site installation
such as homes and small industrial applications, there might also be a certain amount of
infiltration or percolation in the initial period of operation
...
The potential impact of wastewater infiltration to the groundwater, and particularly on-site water supplies, should be evaluated in any event and, if
necessary, lagoon lining may be utilized to alleviate the problem
...

2
...
2
...
Generally, sludge is allowed to dewater and dry to some predetermined
solids concentration before removal, a process that might require 1–3 yr
...
Sludge should be stabilized prior to addition to the lagoon to minimize
odor problems
...

Sludge drying lagoons consist of retaining walls, which are normally earthen dikes
2–4 ft (0
...
4 m) high
...
Ancillary equipment includes sludge feed lines and metering
pumps, supernatant decant lines, and some type of mechanical sludge removal equipment
...


552

Lawrence K
...


In areas where permeable soils are unavailable, underdrains and associated piping may
be required
...
The
pumped sludge is normally stabilized prior to application
...
(0
...
4 m) is achieved
...

(c) Filling the lagoon to a desired sludge depth and then permitting it to dewater
...

(d) Removing the dewatered sludge with some type of mechanical removal equipment
...

(f) Repeating the cycle
...
2
...
2
...
Applications
The “technology” of evaporation is well developed in terms of scientific understanding
and application of climatological and meteorologic data
...

2
...
2
...
Sludge lagoons may require
provisions to add makeup water to maintain a minimum depth during dry, hot seasons
...

2
...
3
...

Lagoons consume no chemicals
...

The lagoons can serve as a buffer in the sludge handling flow stream
...

(e) Organic matter is further stabilized
...

(g) If land is available, lagoons have a very low capital cost
...

(b) There is potential for pollution of groundwater or nearby surface water
...


Evaporation Processes

553

(d) Lagoons are more visible to the general public
...

(f) Rational engineering design data are lacking to allow sound engineering economic analysis
...
3
...
3
...
Target Process Performance
The performance of evaporation lagoons is necessarily site-specific; therefore, the
following data are presented on the basis of net annual evaporation rate that may exist
in a certain area:
Net annual evaporation
evaporation–precipitation
(in
...
1
6
...
4
12
...
9
37
...

Lagoon dewatering of sludges does not usually result in fork-liftable sludge
...
Sludge is first dewatered in a lagoon for 1 yr
...

2
...
2
...
A detailed discussion of these factors follows
...
3
...
1
...
Proper lagoon design, therefore, requires climatic information
concerning:
(a) Precipitation rate (annual and seasonal distribution)
...

(c) Temperature extremes
...
3
...
2
...
6 × 10–4 to 5
...
/s
(4
...
4 × 10 –3 cm/s) and the bottom of the lagoon should be a minimum of
18 in
...


554

Lawrence K
...


2
...
2
...
SLUDGE CHARACTERISTICS

The type of sludge to be placed in the lagoon can significantly affect the amount and
type of odor and vector problems that may be produced
...

2
...
2
...
LAGOON DEPTH AND AREA

The actual depth and area requirements for sludge drying lagoons depend on several
factors, such as precipitation, evaporation, type of sludge, volume, and solids concentration
...
2–2
...
A minimum of two separate lagoons, or even three lagoons, is provided
to ensure availability of storage space during cleaning, maintenance, or emergency
conditions
...
3
...
5
...
Lagoon dikes should have a slope of 1:3, vertical to horizontal, and should be
of a shape and size to facilitate maintenance, mowing, passage of maintenance vehicles
atop the dike, and access for the entry of trucks and front-end loaders into the lagoon
...

Return must exist for removing the surface liquid and piping to the treatment plant
...

2
...
2
...
HYDRAULIC LOADING
The hydraulic loading is the primary sizing criteria for an individual home total-retention
lagoon
...

(b) Evaporation rates (10-yr minimum of monthly data)
...


The rate of wastewater flow is expected to be in the range of 50 gal per capita per
day, depending on the individual site location
...
A 12-mo mass balance should be
utilized to properly determine design sizing
...

2
...
2
...
MONITORING DESIGN

Table 1 summarizes the process variables, measurements, and the monitoring instruT
ments recommended by the US Environmental Protection Agency (US EPA)
...
Because of the longer retention of water in lagoons, sludge stabilization is necessary to minimize noxious odors
...
The design should provide for at least two, or even three, lagoons
having a maximum depth of 4 ft
...
A solid loading rate of about
2
...


Evaporation Processes

555

Table 1
T
Process Variables, Measurements, and Instruments of Sludge Evaporation Lagoons
Process variables

Measurements

Feed sludge

Flow

Pressure
Density

Lagoon contents

Moisture content

Instruments
Venturi with diapragm sensors
Magnetic
Doppler
Pump displacement
Bourdon with cylindrical seal
Nuclear
Optical
Ultrasonic
Portable ohmmeter
Lab test
Transport displacement
Static

Harvested sludge Flow (volume)
Weight
Supernatant and
surface runoff
Weather
Wind speed [15 ft (4
...
6 m)] above ground Wind vane
Temperature [5 and 25 ft (1
...
6 m)]
above ground
Relative humidity
RTD with solar shield
Thermistor with solar shield
Rainfall
RTD with lithium chloride
Solar radiation
cloth (wet bulb temperature)
Tipping bucket
Thermophile
Atmospheric
Odors
Portable olfactometer
monitoring
Source
r : US EPA
...
3
...
Environmental Impact and Energy Consumption
Process reliability is good
...
Potential odors, health hazards, and large land area requirements may
adversely affect surrounding property value
...
Where pumping is required and
assuming a wire to water efficiency of 60%, using the following expression would
approximate energy requirements:

kwh/yr = 0
...
4
...
4
...
Construction Cost
The US EPA published information on capital cost of constructing sludge lagoons
...
21 (January 2002 Cost), typical excavation
and liner costs associated with a two-bedroom residence are as follows:

556

Lawrence K
...


Item

Unit price

Cost
US $

Excavation and hauling (750 yd3)
Liner, 10 mil PVC (21,000 ft2)
Supervision and hand labor

$1
...
28/ft2
––

1472
5964
2117

Total

9553

To the above must be added costs for land, fencing, septic tank, and ancillary items
...
4
...
Operating Costs

Septic tank pump out is the only energy cost
...
82/yr
...
The requirements
include periodic removal of solids and minor maintenance requirements, such as dike
repair and weed control
...

3
...
1
...

However, thermal evaporation precedes sludge drying in several processes
...
Standard chemical engineering treatises examine evaporation in further detail (8–10)
...
Single-effect evaporators are subdivided into short-tube, longtube, and agitated-film evaporators
...

A vertical, short-tube evaporator is shown in Fig
...
A bundle of short tubes (A), 4–8 ft
long and 2–4 in
...
Steam condenses outside the tubes causing boiling of the liquor
...

Concentrated liquor is removed from the bottom of the evaporator (C) and liquid vapor
is removed at (D)
...


Evaporation Processes

557

Fig
...
A vertical short-tube evaporator
...


Short-tube evaporators are being replaced today by long-tube evaporators to achieve
a higher heat transfer coefficient (1)
...

Connection is arranged so that the vapor from one evaporator serves as the heating
medium for the next one, as shown in Fig
...
A vacuum is established in the last stage
to remove noncondensed vapor from the system
...

This arrangement results in the spreading of the pressure difference between inlet steam
and final outlet condensate over all stages
...

Each stage operates as a single-effect evaporator with its own temperature-driving
force and heat-transfer coefficient, corresponding to the pressure drop in that stage
...
The inlet steam pressure and the output condensate pressure are also fixed
...
The composition of the
final concentrated liquor can be changed by simply adjusting the flow rate of the feed
...

Evaporators often operate under vacuum to decrease the boiling point of water or solvent
...
Wang et al
...
3
...
CI, CII, CIII, condensate values; FI, FII, FIII, feed valves; J, Air
Injector and Condenser; P and T,
T pressure and temperature for each effect
...
Vacuum evaporation is important for heat-sensitive materials not only to achieve
better heat transfer, but also to avoid decomposition or alteration of these materials at
elevated boiling temperatures
...

Vacuum evaporation has been used in vitamin B12 production from wastewater
sludge in Milwaukee (11)
...
The Bell–Fons process uses evaporation to precipitate ferrous sulfate monohydrate and to recover sulfuric acid from the pickling liquor of steel mills (12)
...

Celanese Chemical Corporation at Bishop, Texas has developed a solar evaporation
process for treatment of its wastes from the production of organic chemicals
...
Over
65 plants exist worldwide, including an 180,000 gal/d (692 m3/d) plant for treating
4%-solids activated sludge from the Coors Brewery and a 264,000 gal/d (1000 m3/d)
plant for a 2%-solids wastewater effluent at Hiroshima (13)
...
g
...
2 fuel) helps maintain fluidity of the sludge through all stages and minimizes
corrosion and scale formation in the equipment
...
45 lb/lb H2O at about 50 psig for a four-effect unit
...


Evaporation Processes

559

3
...
Process Applications and Limitations
Although the man-made evaporators are technically feasible for water evaporation,
they are generally only economically feasible when the dried sludge can be sold as fertilizer or used as vitamin- and protein-enriched animal feedstock
...
More detailed evaporation process applications are discussed in Example 9 (Section 4
...

Evaporation can greatly reduce the volume of wastewater requiring disposal
...
In the electroplating subcategory of the metal finishing industry, evaporation has
the advantage of permitting recovery of a wide variety of plating and other process chemicals
...
However, the
recovery of waste heat from many industrial processes to provide a source of heat can alleviate the costs
...
Another limitation is that, in some cases, pretreatment may be required to
remove solids and/or bacteria that tend to cause fouling in the condenser or evaporator
...
However, it has been
demonstrated that fouling on the heat transfer surfaces can be avoided or minimized for
certain dissolved solids by maintaining a seed slurry, which provides preferential sites
for precipitate deposition
...

Steam distillable impurities in the process stream are carried over with the product
water and must be handled by pre- or posttreatment, if they cannot be tolerated
...
When ponding is used, the solid
residues generated must also be disposed of
...
3
...
The necessary heat-transfer rate can be calculated on the basis of the
required evaporation rate
...

3
...
1
...
Heat is transferred from the steam in the evaporating liquid through a
heating surface
...

The transferred heat raises the temperature of the liquid to its boiling point, corresponding to the absolute pressure in the evaporator, and supplies the latent heat

560

Lawrence K
...


Fig
...
Dependence of the specific resistance on pressure head
...
If the feed is at a temperature above the boiling point, flash
evaporation occurs
...
Conversely, the boiling point of solutions at a given pressure is higher than
that of pure water
...

In an evaporator loaded with an appreciable depth of liquid, the boiling point
increases with the depth because of the existing liquid head
...

The heat-transfer coefficient expresses the facility of heat flow for a particular design
and operation
...

If scale forms inside and/or outside the tube walls, additional resistance terms (Fig
...
(2)
...

3
...
2
...
5
...
Short tube
a
...
Calandria type
2
...
Natural circulation
b
...
Coil evaporators
4
...


Fig
...
Schematic diagram of a single-effect evaporator
...

If wF = the weight fraction of water in the feed, wL = the weight fraction of water in
the concentrated liquid, and y = the weight fraction of evaporated water
A material balance for water yields
wFF′ = wLL′ + yV′
V

(4)

QS = S′(H
HS – HC)

(5)

The heat supplied by the steam is

562

Lawrence K
...


where Qs = rate of heat transfer by steam, BTU/h; S′ = the weight of steam supplied to
the evaporator lb/h; and Hs and Hc = the enthalpies of steam and condensate, respectively, BTU/lb
...

A heat balance for the condensing liquid gives
QL = (Heat out, in vapor and thick liquid) – (Heat in, in feed)

(6)

QL = (L′H
HL + V′
V HV) – F′H
HF

(7)

where QL = rate of heat transfer to liquid, BTU/h; HF = enthalpy of feed, BTU/lb; HL =
enthalpy of thick liquid, BTU/lb; and HV = enthalpy of vapor, BTU/lb
...
(3),
S′(H
HS – HC) = L′(H
HL – HF) + V′(
V HV – HF)

(8)

Normally, low-pressure steam is used in evaporation
...

3
...
3
...
3)
...
At steady state, this
water vapor will condense around the tubes of the second stage to vaporize an almost
equal amount of water in stage II
...

The heat exchanged in stage II is
QII = UII AII ΔT
TII

(10)

From the operation of this stage it follows that the amounts of heat exchanged in effects
II and I are almost equal
...

Usually, the heating surface areas of all effects are equal for construction economy,
therefore,
Ui 'Ti

Q A Constant

(13)

Equation (13) suggests that the temperature drops are inversely proportional to the overall heat-transfer coefficients in each effect, e
...
,
'TI 'TII

UII UI

(14)

Evaporation Processes

563

It should be emphasized that Eqs
...
The total heat
exchanged in an N-ef
N ffect evaporator is the sum of all Qi:
S

QT

S

¦ Qi
i 1

¦ U A 'T
i

i

(15)

i

i 1

If all Ai and Ui are equal to a constant value A and U, respectively, then
S

QT

UA¦ 'Ti

UI AI 'TT

(16)

i 1

TT = the total temperature drop across the system
...
Therefore, the
capacity of a multiple-effect evaporator is no better than that of an equivalent singleeffect unit
...

However, significant steam economy is achieved
...
In a single-effect evapN-ef
orator, each pound of steam vaporizes only about 1 lb of water
...

4
...
1
...
The
evaporator operates at 0
...
If the feed rate is 10,000 lb/h
at 70°F, and the heat-transfer coefficient is 400 BTU/ft2 h °F, calculate: (a) the amount of
steam required; (b) the amount of water evaporated per pound of steam (economy); and
(c) the heating surface area
...
The specific heat capacity of the feed sludge is CP,F = 0
...

•

•

•

Solution:
Material Balance:
Water in feed:

92
8

11
...
85 lb water / lb solids
Water evaporated: = 9
...
08 × 9
...
(3)–(7) rearranged
to give
S′ΔH
Δ v = (F′
F –L′)Hv + L′H
HL – F′H
HF
(17)
where ΔH
Δ v is the latent heat of vaporization of steam at 10 psig
...
Wang et al
...

The enthalpy of the vapor Hv with respect to the thick liquor now represents the latent
heat of vaporization at the operating pressure in the evaporator
...
4°F
Δ v = Hs – Hc = 952
...
95 psia,
TL = 100°F
Hv = 1037 BTU/lb
With the feed entering at TF = 70°F, the steam rate is
Sc

(10, 000  2380)1037  10000 u 0
...
6

8572 lb/h

Steam Economy
Vc
Sc

7720
8572

0
...
6
400( 239
...
4 ft 2

4
...
Example 2
Sludge is concentrated in a triple-effect evaporator to recover vitamin B12
...
If the overall heat
transfer coefficients are 400, 320, and 240 for the first, second, and third effects, respectively,
estimate the liquor boiling temperature in each stage
...


Solution:
Assuming that all effects have the same heating surface area, Eqs
...
8qF

and
'TIII

125
§ 1 ·
¨
¸
1
1 · © 240 ¹
§ 1


© 400 320 240 ¹

53
...
8 = 163
...
3
...
5-ft diameter (max
...

Average precipitation, in
...
54
1
...
79
1
...
26
1
...
Wang et al
...

Net Evaporation, gal/ft2
Evaporation Area, ft2
Net Evaporation, gal

4
...
83
1908
5400

6
...
23
1319
5580

8
...
02
1076
5400

(Note: 1 in
...
6233 gal/ft2)

4
...
Example 4
Discuss the ffollowing for the sludge evaporation lagoon in Example 3:
(a)
(b)
(c)
(d)

Structural elements
...

A cable and scraper system for the sludge evaporation lagoon
...


Solution:
(a) Structural Elements: The retaining walls for drying lagoons are typically earthen dikes
0
...
4 m (2–4 ft) high with a side slope of 1:3
...
5-ft diameter evaporation
lagoon is technically feasible for efficient water evaporation
...
The last may include trucks, front-end loaders, bulldozers, or draglines, depending on the size of the operation
...
These lagoons share a common problem with other air drying processes in
that a surface crust forms early in the evaporative stage, which then restricts further
evaporative water losses
...
Similar
equipment and procedures can be used in drying lagoons, if the depth of sludge permits
...

(c) Larger scale facilities may use cable and scraper system as shown in Fig
...

(d) Operation and Maintenance: The routine operational activities consist of sequential
sludge applications and decantations until the lagoon contains the design volume of
sludge
...
Sludge removal is labor intensive but occurs infrequently
...
Some
sludge drying lagoons may require insect and odor control
...


4
...
Example 5
Obtain the annual evaporation data for the United States
...


Solution:
Annual evaporation data for the contiguous United States are presented in Fig
...
The compiled annual evaporation data will be

Evaporation Processes

567

Fig
...
Cable and scraper system for sludge drying lagoons
...
For better lagoon design
and operation, the environmental engineer in charge of design and operation should obtain
the local 10-yr monthly evaporation and precipitation data and perform calculations similar
to Example 3
...
6
...


Solution:
The manufacturers of commercial prefabricated evaporators can be found in refs
...


4
...
Example 7
Briefly define “evaporation process,” discuss the process energy source, and explain the
difference between “evaporation” and “drying” from technical viewpoints
...

Evaporation is a concentration process involving removal of water from a solution by
vaporization to produce a concentrated residual solution
...
The process
offers the possibility of total wastewater elimination with only the remaining concentrated
solution requiring disposal and also offers the possibility of recovery and recycle of useful
chemicals from wastewater
...
When the vapor is a mixture, no attempt normally
is made in the evaporation step to separate the vapor into different components
...
8
...
The text divides
the evaporation process into natural evaporation and man-made evaporation
...


Solution:
The evaporation process can be divided into the broad categories of steam evaporation and
solar evaporation
...
7
...


Evaporation Processes
1
...
The process is carried out either at a pressure less than atmospheric
(vacuum evaporation) or at atmospheric pressure (atmospheric evaporation)
...
All of the water vapor is condensed
and, to maintain the vacuum condition, noncondensible gases (air in particular) are
removed by a vacuum pump
...
For example, in double-effect evaporation, the water vapor from the first
evaporator is used to supply heat to a second evaporator operated at a lower pressure
...
Thermal
or mechanical vapor recompression is another energy-conservation technique
available, which enables heat transfer from the condensing water vapor to the
evaporating wastewater
...
A brief description of the two follows:
(i) Submerged tube (In most commonly used submerged tube evaporators, the
heating and condensing coils are contained in a single vessel to reduce capital
cost
...
Wastewater accumulates in the bottom of the vessel and is
evaporated by means of submerged steam coils
...
The condensate then drips off the condensing coils into a collection trough that carries it
out of the vessel
...

(ii) Rising film (The major elements of the rising film evaporator are the evaporator, the separator, the condenser, and the vacuum pump
...
Liquid from the separator enters the steam-jacketed evaporator tubes
and is partially evaporated
...
The vapor entering the separator flows
into the condenser where it is condensed as it flows down through the condenser
tubes
...
Thus, the liquid seal provided
by the condensate keeps the vacuum in the system from being broken
...
Wastewater is evaporated by using it
to humidify air flowing through a packed tower
...

2
...
Successful implementation depends on favorable climatic conditions
(not evaporation) and on the availability of land
...
In some instances where impoundment is not practical for the total
wastewater discharge, impoundment of smaller, highly contaminated wastewaters
from specific processes may afford significant advantages
...
Wang et al
...
The wastewater is sprayed under pressure
through nozzles producing fine aerosols, which are evaporated in the atmosphere
...
Temperature, wind speed, spray nozzle height, and
pressure are all variables that affect the amount of wastewater that can be evaporated
...
9
...
The technology is proven and
its application is expanding
...
This chapter’s text places emphasis on sludge evaporation/
drying
...


Solution:
Evaporation can be used for a variety of purposes including dehydration, recovery, separation,
and concentration
...
The following industries use evaporation
methods on a widespread basis for waste treatment and/or recovery of chemicals:
(a) Metal Finishing
(b) Explosives Manufacturing
(c) Timber Products Processing
The following industries use evaporation on a limited basis:
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)

Inorganic Chemicals Manufacturing
Aluminum Forming
Battery Manufacturing
Pharmaceutical Manufacturing
Nonferrous Metals Manufacturing
Organic Chemicals Manufacturing
Paint and Ink Formulation
Petroleum Refining
Rubber Processing
Textile Mills

In the metal finishing industry, evaporation is a common technology for recovery of plating
chemicals from rinse water
...

The water vapor is condensed and returned to the rinse tank
...
” The strong black liquor is then burned to recover heat and chemicals
...
10
...
2 MGD has been reliably
serving 10,000 residents and tourists in the town of Lenox, Massachusetts, USA, since
July 1982
...
It substantially improves upon the conventional
flocculation, sedimentation, and filtration system in performance, capability, operation,
maintenance, and energy use (19–42)
...
Because of the Lenox flotation plant’s compact design (diameter = 22 ft;

Evaporation Processes

571

Table 4
T
Investigation of Sludge Production, Lenox Water Treatment Plant, November, 1982
Influent
f
flow
(gpm)

Sludge flow
(gpm)

Sludge TSS
(mg/L)

11/01/82
11/02/82
11/03/82
11/04/82
11/05/82
11/06/82
11/07/82
11/08/82
11/09/82
11/10/82
11/11/82
11/12/82
11/13/82
11/14/82
11/15/82
11/16/82
11/17/82
11/18/82
11/19/82
11/20/82
11/21/82
11/22/82
11/23/82
11/24/82
11/25/82
11/26/82
11/27/82
11/28/82
11/29/82
11/30/82

429–545
390–545
390–519
519
490–519
391–519
391–519
391–535
391–535
391
391–535
535–536
391–536
536
391–536
391–527
527
387–527
387–536
536
387–547
547
388–547
388–595
477–481
476–481
471–476
471–500
479–500
479

3
2
2
4
5
5
6
3
4
5
2
2
4
2
5
4
4
4
3
3
3
3
8
3
5
7
3
1
2
2

3271
1334
2611
3051
1771
1771
1771
1771
1029
1029
1440
2555
3180
1035
3810
948
488
3000
1303
1548
1548
1258
2732
983
1346
4621
7705
12,535
3211
3211

Range
Average

387–595

1–8
3
...


depth = 6 ft), its equipment installation cost, housing cost, heating cost, land requirement,
etc
...

The Lenox Water Treatment Plant has been using a sludge evaporation lagoon (sludge
drying lagoon) for thickening its alum sludge
...


Solution
(a) Sludge Generation: An investigation of sludge production at the Lenox flotation
plant was conducted in November, 1982, and the results are presented in Tables 4
and 5
...
Wang et al
...
0
0
...
4
1
...
0
150
...
0
150
...
84
0
...
63
217
...
84
290
...
1 gpm = 1 gallon per minute =
3
...
785 liters per hour;
1 MGD = 1 million gallons per day = 3
...


Table 6
T
Chemical Treatment Summary
Month
in
1982
July
August
September
October
November
December
Total
(Average)

Water
treated
(gal)
11,622,900
31,480,646
20,461,473
24,471,287
20,351,372
21,113,800
129,501,478

Alum
Alum
Alum
Polymer Polymer Polymer
dosage
dosage
residue
dosage dosage residue
(mg/L Al2O3) (lb)
(mg/L Al2O3) (mg/L)
(lb)
(mg/L)
1
...
75
2
...
27
2
...
39
(2
...
60
723
...
75
463
...
76
597
...
23

0
...
50
0
...
37
0
...
32

0
0
...
02
0
...
84
0
...
38)

(0
...

1 gal = 3
...


0
120
...
12
22
...
16
77
...
16

0
0
...
004
0
...
07
(0
...
9
30,425
3420
27,005
<0
...

*The settled lagoon sludge was accumulated in the period from May 21 to Nov
...

**Total suspended solids and volatile suspended solids are average values of eight sludge samples
...

BD = Below detection limit of AA
...
It can be seen that the plant’s chemical consumption was
much lower than that of a comparable conventional water purification plant
...
8 dry lb/d/MGD, as
shown in Table 5
...
It is believed that the
low sludge production rate of a conventional plant is caused by discharge of filter
backwash wastewater, without recycle
...
8 instead of
75 dry lb/d/MGD) because almost all sludges are captured by dissolved air flotation
...
7% of influent flow
rate
...

(b) Sludge Evaporation Performance: The data documented in Table 7 are for sludge
handling and disposal (30,31,41,42)
...
63 gpm and 2600 mg/L, respectively
...
3 gpm
...
The analytical data in
Table 5 are for the settled lagoon sludge accumulated in the period from May 21 to
November 21, 1982
...

The lagoon sludge contained mainly inorganic fixed suspended solids (27,005 mg/L),

574

Lawrence K
...

Table 8
T
Sludge Evaporation and Monitoring at Lenox Water Treatment Plant

Date

Lagoon
flow
(gpm)

11/04/82
11/07/82
11/08/82
11/09/82
11/20/82

3
...
0
5
...
0
3
...
6
4
...
3
5
...
2

Lagoon and filter effluent
Turbidity
TSS
Color
(NTU)
(mg/L)
(unit)
1
...
6
1
...
7
3
...
4
0
...
9

4
5
5
5
6

Adapted from Krofta and Wang (30,31)
...
785 liters per
minute
...
All heavy
metal contents were extremely low
...
The November 1982 lagoon operational
data in Table 8 show that the slow sand filter effluent was as clean as reservoir raw
water
...

A Discharge Permit for discharging the lagoon effluent from the Lenox Water
Treatment Plant to a nearby stream has been granted by the Commonwealth of
Massachusetts, Department of Environmental Quality
...

The following paragraphs introduce the physical structures of the sludge evaporation
lagoon system
...
63 gpm
...
Its size is approx 31 ft W
× 47
...
75 ft W × 42
...
Its depth is about 6 ft
...
The
lagoon overflow rate and weir overflow rate are less than 500 gpd/ft2 and less than
2000 gpd/ft, respectively
...
5–0
...
of small-diameter gravel under
the sand, and 9 in
...
Its loading rate
is equal to or less than 15 gpd/ft2
...
The filter effluent is as clean as the reservoir raw water
...

The lowest elevation of the sludge evaporation lagoon has been kept above ground
water level to avoid being overflowed with ground water
...
The City of Albany’s
evaporation lagoon system involves the use of natural evaporation, freezing, thawing,
and sedimentation processes for treatment of combined filter backwash water and
sedimentation waste sludge
...
°F
Specific
f heat capacity of thick liquor, BTU/lb
...
h
...
h
...
hr
...
h
...
Wang et al
...
G
...
Sakellaropoulos, Drying and evaporation processes, in Handbook of Environmental
Engineering, V
Vol
...
K
...
C
...
), Humana Press, Totowa, NJ, 1986,
pp
...

2
...

3
...

4
...

5
...

6
...

7
...
J
...
T
...
), Air P
Pollution Engineering Manual, Air and Waste
Management Association, Van Nostrand Reinhold, New York, 1992
...
W
...
Badger and J
...
Banchero, Introduction
r
to Chemical Engineering, Chapter 10
...

9
...
L
...
C
...

10
...
H
...
), Chemical Engineer’s Handbook, McGraw-Hill, New York, 1963
...
R
...
Leary, Production of vitamin B12 from Milorganite
...

r of 9th Purdue Industrial
Waste Conf
...
173, 1954
...
E
...
Besselievre, T
The Treatment of Industrial Wastes, McGraw-Hill, New York 1969
...
J
...
Yaminmota, J
...
Schnelle, and J
...
O’Donnell, High nitrogen synthetic fertilizer produced from organic wastes
...

14
...
Public Works 133(5), 333, 334 (2002)
...
Editor, 2002–2003 Industrial and municipal wastewater technology buyer’s guide: evaporators
...

16
...
P
Pollution Engineering 31(11), 40, 41 (1999)
...
Editor, 2002 Buyer’s guide: evaporation equipment
...

18
...
Chemical Engineering 107(9), 310–316 (2000)
...
M
...
K
...
of Commerce,
National Technical Information Service, Springfield, VA, March, 1982
...
M
...
K
...
S
...
for Potable Water Treatment, Report #
PB82-220690, US Dept
...

21
...
Krofta and L
...
Wang, Alternative
r
Water Treatment Systems Using Flotation Technology,
Report # PB82-211400, US Dept
...

22
...
Krofta and L
...
Wang, Potable water treatment by dissolved air flotation and filtration
...

23
...
Krofta and L
...
Wang, Startup and Continuous Operation of Lenox Water Treatment
Plant, Report # PB85-182616/AS, US Dept
...

24
...
Krofta and L
...
Wang, Data of Lenox Water Treatment Plant, Report # PB84192061, US Dept
...


Evaporation Processes

577

25
...
Krofta and L
...
Wang, Development of innovative Sandfloat systems for water purification and pollution control
...

26
...
Krofta and L
...
Wang, Design, Construction and Operation of Lenox Water Treatment
Plant, U
...
A
...
of Commerce, National
Technical Information Service, Springfield, VA, 1983
...
M
...
K
...
S
...
Project Documentation, Report # PB83-164731, US Dept
...

28
...
Krofta and L
...
Wang, Over One-Year Operation of Lenox Water Treatment Plan–Part 1
...
of Commerce, National Technical Information Service,
Springfield, VA, July 1983
...
M
...
K
...
of Commerce, National Technical Information Service,
Springfield, VA, July, 1983
...
M
...
K
...
JJournal of New England Water Works Association
249–264 (1985)
...
M
...
K
...
JJournal of New England Water Works Association
265–284 (1985)
...
M
...
K
...
of Commerce, National Technical Information Service, Springfield,
VA, Oct
...

33
...
Krofta and L
...
Wang, Monitoring and Control of Lenox Water Treatment Plant, Lenox,
Massachusetts, Report # PB84-192079, US Department of Commerce, National Technical
Information Service,
...

34
...
Krofta and L
...
Wang, Development of innovative flotation-filtration systems for water
treatment, Part A: First full-scale Sandfloat plant in US
...
V
Vol
...
1226–1237, Aug, 1984
...
M
...
K
...
Proceedings
r
of American
Water Works Association Water Reuse Symposium III
...
3, pp
...

36
...
Krofta and L
...
Wang, Application of dissolved air flotation in water purification
...
of Commerce, National Technical Information Service, Springfield, VA, Nov
...

37
...
Krofta and L
...
Wang, Recycling of filter backwash water and alum sludge for reuse in
water treatment Plants
...

38
...
K
...

UNIDO Training Manual No
...

39
...
K
...
OCEESA JJournal 13(1),
12–16 (1996)
...
L
...
Wang, Water and waste treatment using advanced dissolved air flotation
...

Feb
...

41
...
K
...
The
T
Sixth Annual Water Treatment Technical Conference, Saratoga Springs, New York, April,
1991
...
Wang et al
...
L
...
Wang, Innovative and cost-effective Lenox Water Treatment Plant
...

43
...
J
...
June
...
geog
...
bc
...
html, 2003
...
L
...
Wang, E
...
Fahey, and Z
...
K
...
T
...
K
...
), Humana Press, Inc
...
431–500 (2005)
...
R
...
Sonntag, C
...
J
...


Evaporation Processes

579

Appendix: Steam T
Tables (45)
Temperature (°F)
T
100
230
240

Pressure (psia)

Δ v (BTU/lb)
ΔH

Hv (BTU/lb)

0
...
781
24
...
98
958
...
27

1105
...
12
1160
...
95 psia corresponds to a TL of 100°F, with ΔH
Δ v = 1037 BTU/lb
...
696 psia
...
4°F and 952
...
8 psig
corresponds to 22
...
Interpolation yields a TL of 235°F

---