Page 196 - Environmental Control in Petroleum Engineering

182 Environmental Control in Petroleum Engineering

1986). A high molecular weight polyaerylamide polymer has been
found to be effective to flocculate solids in water-based drilling muds,
and a nonionic polyethylene oxide with a high molecular weight
nonionic polyacrylamide polymer has been found to be effective for
oil-based muds (Sharma and Smelley, 1991), Chemically enhanced
centrifugation has been successfully used to remove solids from both
drilling mud and produced water (Malachosky et al., 1991).
Suspended solids can also be flocculated with alternating current
eiectrocoagulation (Farrell, 1991). In this process, a metal hydroxide
is added to the water and an alternating current is used to overcome
the electrostatic repulsion charges on the particles. Iron and aluminum
hydroxides have been successfully used.

6.1.4 Removal of Dissolved Solids

Most wastewater also contains dissolved solids, particularly salt,
hardness ions (calcium and magnesium), and heavy metals. A variety
of methods are available to treat these waters. The methods vary
considerably in cost and effectiveness,

Ion Exchange

Ion exchange (water softening) is an effective way to remove
hardness ions from water. In most cases, the hardness ions (calcium
and magnesium) are replaced with sodium ions. The removal of
hardness ions is necessary for many processes because these ions
readily precipitate and form a hard scale that can foul equipment.
There are two major ion exchange resins (substrates) that are
commonly used: strong acid resins, using sulfonic acid, and weak acid
resins, using carboxylic acid. Strong acid resins can be regenerated
simply by flushing with a concentrated solution of sodium chloride.
Weak acid resins, however, must be regenerated by flushing with a
strong acid-like hydrochloric or sulfuric and then neutralizing with
sodium hydroxide.
In some cases, the water can simply be passed through a bed of
clay particles. The cation exchange capacity of most clays is very high,
which allows them to trap and retain relatively high concentrations of
dissolved metals. Activated alumina filtration is also an effective ion
exchange media for metals like lead, mercury, and silver.