Page 199 - Membranes for Industrial Wastewater Recovery and Re-Use

168 Membranes for Industrial Wastewater Recovery and Re-use

different temperatures and/or using different cleaning chemicals depending on
the residues that need to be removed from the equipment. All cleaning cycles
normal finish with one or more rinses using drinking water then a final rinse
using PW or WFI.
Finally, water may be “dumped” from the system periodically as part of a
standard procedure. Until quite recently it was standard practice for all WFI to be
“dumped” after 24 hours if it was not used in production so that all water could
be classed as “freshly produced”. This procedure is not commonly followed now
but where it is carried out the water being dumped is of a much higher quality
than the drinking water used to produce more WFI. Water is also dumped to
regulate the load on the sanitiser where sanitisation by heating to 80°C is
conducted. Such water is also of a much higher quality than the mains water
used as the feed for the purification system.
In the UK and Ireland the majority of the PW and WFI water systems produce
water at between 500 and 5000 1 h-l, although there are some notable
exceptions where generation rates are significantly higher. There is often a PW
and sometimes a WFI water system installed in each building on a large site: one
UK pharmaceutical site has approximately 30 PW and WFI water systems on a
single site. On smaller sites one generation plant can supply a number of
buildings or manufacturing areas via distribution pipework systems.
Since every production process is different, requiring different volumes of
water, producing different quantities of effluent with different levels and types
of contaminant, it is not possible to estimate typical water usage figures.
However, to illustrate the water volumes that might typically be involved a
hypothetical system can be considered.
PW and WFI systems in Europe are typically based on generation flow rates of
0.5-5 m3 h-l. There are some notable exceptions utilising higher flow rates and
typical system sizes in America also tend to be higher. This hypothetical system is
based on a PW production rate of 3000 1 h-l and 1000 1 h-l WFI, with a daily
process usage of 24 000 1 of PW and 8000 1 of WFI. The PW system will operate
continuous in recirculating mode when no water is being made up to the storage
vessel while the WFI still will operate in a stop/start mode. The approximate
quantities and qualities of effluent will be in the ranges shown in Table 3.38.
Based on these approximate estimated volumes the maximum volume of
effluent water that could be reclaimed is around 3 1 m3 day-l. If the water were
passed to a purpose-built reclaim system this volume would rise to around 70
m3 day-’. In practice the water that arises from some of the more contaminated
CIP rinses would probably not be reclaimed.
If the main technology used in the reclaim system is reverse osmosis then
the likely maximum quantity of reclaimed water which could be returned to the
purification system as “raw” water would be around 23 m3, based on a recovery
of 75% from the RO treatment plant. Based on current costs of around €1.6 per
m’ ($2.57 per m3) for purchase of potable water and disposal of effluent water,
reclaiming this quantity of water would save only around E37 [$59.5] per day.
The operating costs associated with the reclaim system, including maintaining
the validation documentation necessary, is estimated to be over E50 [$80.4] per