Veolia Water Technologies Business Development Manager, Kalpesh Shah, explains how evaporation can help smaller cosmetics facilities to save money on wastewater disposal.
Energy Managers are starting to realise that wastewater from
cosmetic production is a potential source of money instead of an unwelcome
expense. Evaporation for smaller cosmetics manufacturing facilities that
currently dispose of liquid waste offsite will reduce wastewater disposal costs
and offer opportunities for recovering raw materials (such as disinfectants,
proteins and glycols) as well as recycling water. The article will
explain how evaporation works and demonstrate a customer that is using the
How Does It Work?
Evaporation is a very old technology – think extracting salt from
sea water – and this concept has been applied in many industries but, in the
context of wastewater treatment it has all too often been dismissed as
uneconomic. However, things are changing. As alternative disposal routes such
as sewer discharge and landfill become more expensive, evaporation is looking
more and more attractive. Offsite disposal of wastes containing Active
Pharmaceutical Ingredients (APIs) and similar ingredients, often involves
incineration or complex chemical treatment: evaporation is a sustainable and
environmentally friendly alternative that can reduce the waste volume by up to
90% giving a significant cost saving.
Cosmetics and pharmaceutical manufacturing facilities that currently
dispose of liquid wastes offsite can use evaporation to minimise operating
costs and recover raw materials including APIs, disinfectants, proteins and
glycols, as well as recycling water. How? Well, evaporators work by converting
water into vapour, which needs heat to overcome the latent heat of evaporation.
This water vapour can then be condensed by cooling to remove the latent heat,
producing distilled water for re-use. What is left behind in the evaporator is
a concentrated liquid, around only 10% of the original volume which
substantially reduces off-site disposal costs.
For this process to work the water has to be at its boiling point
and, at atmospheric pressure, this is 100°C, a temperature which can break down
many pharmaceutical and cosmetic ingredients. The latest generation of heat
pump evaporators operate under vacuum, which means that water boils in the
range of 30-40°C. The resulting low temperature evaporation means that it is
possible to recover even heat sensitive raw materials from wastes.
Heat pump evaporators use a compressor driven refrigerant circuit to
extract the latent heat from the water vapour, which condenses it, and then
transfers it to the liquid to evaporate it. This is a highly efficient way of
recovering the latent heat and means that there is very little additional heat
required for the process. Any additional heat that is required can be provided
by an internal electric heater or an external hot water supply. The result is a
process that uses, typically, 0.15 kWh per litre of distillate.
Forced Circulation or
There are two principal technological options for evaporation:
forced circulation and scraped surface. In forced circulation units, the liquid
is pumped through a heat exchanger to increase the temperature to about 40°C
but, because it is under pumped pressure, it does not boil. The hot liquid then
enters the evaporator body, which is under vacuum, where the liquid “flashes”
to form vapour leaving behind a concentrated liquid stream. The recirculation
velocity maintains turbulent conditions in the heat exchanger tubes to keep the
heat transfer surfaces free from deposits which could adversely affect heat
transfer efficiency. This type of evaporation means that the liquid and vapour
phases are easily separated under gravity, producing the highest distillate
Forced circulation evaporation is about distillate quality, but
scraped surface technology is about minimising the volume of concentrate for
disposal. It can even handle high viscosity or foaming wastes. Scraped surface
is like reducing a sauce in cookery – if you don’t keep stirring it, it is
going to burn. Heat is transferred rapidly by conduction from the cooker
through the bottom of the saucepan to the liquid. The heat is then transferred
from the hot saucepan into the liquid. This hot liquid then moves away from the
heating surface by convection into the bulk of the liquid. As the liquid
viscosity increases, the rate of convection is reduced, so more heat is going
into the liquid than can be removed; with the result that the viscous liquid at
the bottom of the saucepan overheats and burns. Stirring removes the liquid
from the hot saucepan doing the job of convection currents. In a scraped
surface evaporator the internal heat transfer surface is continuously scraped
by a rotating blade that prevents viscous liquids clinging to the surface and
A Case in Point
Looking at a case study will help to explain the difference. A
multinational company with more than 250 manufacturing facilities worldwide,
with their main facility in Italy, manufacture hair care products operating 24
hours a day for six days a week. The plant produces 36TPD (Tonnes Per Day) of
wastewater with a Chemical Oxygen Demand (COD) in excess of 30,000mg/l. This
was originally treated by a membrane bioreactor (MBR) producing a high quality
treated effluent fed directly to a reverse osmosis plant for recovery. The MBR
also produced about 0.5tpd of excess biological sludge. The company’s global sustainability
targets set goals for water and raw materials reduction, which led the facility
to search for an effective solution that would allow them to reduce both water
consumption and MBR sludge production. Initially they installed a small heat
pump evaporator to concentrate high density wastewater for off-site disposal.
This was so successful that they decided to see what other evaporation
technology could be implemented.
After a review of the site operations and wastewater
characterisation, Veolia’s engineers developed a scheme using two stages of
evaporation. The first stage uses a TC30000 FF MVR evaporator to treat 30TPD of
dilute wastewater producing 27TPD of distillate and 3TPD of concentrate, which
is mixed with 6TPD of concentrated process waste and sent to a RW 12000 FF
scraped surface evaporator, which is fed with hot and cold water from the
on-site Combined Heat and Power (CHP) plant. Subsequently this produces a
further 7.5TPD of distillate and reduces the concentrate to only 1.5TPD, which
is taken off-site for incineration. The plant performance is summarised in
TABLE 1 EVAPORATION PLANT PERFORMANCE
Both evaporators are constructed in SAF 2507 super-duplex (austenitic-ferritic) stainless steel and each has a footprint of 14.5m2. The condenser cooling water and hot water for heating the scraped surface evaporator are supplied from the on-site CHP plant.
The combined 34.5tpd of distillate is further treated in the membrane bioreactor (MBR) but sludge production has been reduced from 500kg/day to less than 20kg/day with an improvement in treated wastewater quality resulting from a lower COD loading on the plant.
The new plant slightly increased energy consumption but this was more than compensated for by the recovery of some 96% of the wastewater for reuse and a large reduction in off-site disposal costs. The overall result is a reduction in total treatment costs of 75% giving a payback on the investment in less than a year.
Evaporation can reduce off-site disposal costs and recover not only good quality distilled water but also valuable ingredients. With low capital and operating costs, evaporative technologies, such as Veolia Water Technologies UK’s range of EVALED™ PC heat pump evaporators, the result of three decades of evaporation experience, are now well within the reach of even small cosmetics facilities.