This news article was originally written in Spanish. It has been automatically translated for your convenience. Reasonable efforts have been made to provide an accurate translation, however, no automated translation is perfect nor is it intended to replace a human translator. The original article in Spanish can be viewed at Estudio de descontaminación de aguas residuales de una empresa de transformados metálicos

Carried out in cooperation with the Department of environmental engineering of the metalworking technological Institute (AIMME)

Study of decontamination of waste water of a company's processed metal

Ana María Payá Jorge *. Industrial technical engineer.
Polytechnic University of Valencia15/09/2004

The project involves a review detailed of all pollution-producing processes, assessing the nature and amount of them, to make reasonably measures aimed at correcting and minimization of pollution, based on criteria such as efficiency and performance, production costs, maintenance of the quality of the products, objectives and environmental policies of the company.

The industry referred to in the draft performs his main activity in the sector of processed metal, specifically in the area of furniture and luminaires, consisting of its manufacturing process in the surface treatment of fittings of brass, on the basis of castings by an external company.

Work began making a detailed examination of all the manufacturing processes capable of producing pollutant discharges, finding in each of these points of origin of the contamination, as well as the character of the same. All the independent flows are quantified. It was special care and rigor in this stage of the work, assuming that you for the design of a decontamination treatment is essential to a deep knowledge of production processes.

The realization of the production process will generate a from discharge of acid pickling washes, 4,65 and spontaneously, giving rise to a spill acid under high load in heavy metals such as copper, zinc, nickel and lead from the raw material used, brass.

Copper 57-70 %
Zinc 36-40 %
Nickel 1.5-3 %

The high content of these metals is that the resulting effluent fails to comply with specified in the legislation to be poured, creating the need to establish a physical-chemical system to improve the quality of the effluent to acceptable values to be dumped.

On the other hand, the company has a bath of degreasing ultrasonic, for its high oil content, is not possible to treat with the rest of effluent, making it necessary to apply other cleansing treatment to the bathroom.

All waters from industrial activity are channeled together with domestic sewage to be subsequently made to the network of public sewers through the chest of registration.

The total volume of concentrated pulsed discharge of the ultrasonic degreasing-from basic character is around 11,000 litres per year, placing us in the most unfavourable case.

The total volume of continuous discharge from the rinsing with halogenated, acid and basic nature depending on the section to which it relates, is 183.920 litres per year, resulting in a total volume of landfill of 194.920 l/yearthat is to say, 886 l/day.

From the study in this report, he advised the company to regulate conditions for the disposal of industrial water. Its management, in response to the problems on discharges that currently presents the company, is considered to pour to the municipal sewage the alternative most appropriate, since in this way avoiding additional costs such as Manager or to an external WWTP wastewater transport, and can thus carry out growth strategies of the company without too high costs.

Techniques of waste minimisation

As we have already seen, waste water of the company presented three problems of disposal which we will have to remedy by means of the methods proposed. These three problems, as revealed by analysis of waters, are:

Concentrations of copper and zinc
pH
Nitrates

Therefore, the objectives of the corrective measures that apply on spills fluids must be:

Reduce the concentrations of the characteristic parameters of discharges to limits that are not detrimental to the environment and which conform to the standard limits.
To minimize the possible production of waste in the treatment of waste.
Ensure minimum costs of maintenance of waste treatment facilities.

For the achievement of these objectives, proposed the design of a physical-chemical treatment of all discharges described in previous sections, in order to purify waste waters from the appropriate section before his discharge, so that their characteristic parameters are not harmful to the environment and comply with the limits that set out in the regulations.

However, the physical-chemical procedure is not able to remove nitrate from waste water itself. The reason lies in the range of pH's work. Nitrates are a very high degree of solubility, so hardly a removal method based on the precipitation of ions forming salts, such as the conventional physical-chemical treatment, will not be effective. Why should resort to other methods of disposal such as reverse osmosis or ion exchange.

Then we cite each of the proposed remedial measures and will describe them in detail.

Minimization of the effluent from the current rinsing of the section of pickling/desbarnizado

The company has a section of pickling/desbarnizado where defective painted parts are submerged in a bath with chlorinated solvent and are subsequently enjuagadas to eliminate the possible remains of a current rinse solvent...

As the legislation in force completely prohibits the discharge of effluents having halogenated solvent remains, this stage of the production process should be modified to comply with the required regulations.

This amendment will be to convert the current rinsing in a watertight rinse, placed a rack on the bath of desbarnizado where she is mailed desbarnizadas pieces so that they drain the bath film attached.

In this way, is minimizarán the loss of solvent drip and clean waterproof rinsing will be maintained for a long time.

When rinsing is polluted enough and may not adequately fulfill its function, it must then be managed through an authorised Manager.

A deep knowledge of production processes is essential for the design of a treatment of decontamination

Minimization of the effluents from the ultrasonic degreasing bath

Degreasing ultrasonic bath is used in order to eliminate the remains of oils, shavings and remnants of polishing pastes that pervades the pieces after going through the stage of machining; in such a way that they are a surface clean and appropriate for the subsequent processes. It's a bathroom consisting of surfactants which, under the effect of heat, and ultrasonic flow allows the separation of the oil layer attached to the piece. Once produced the separation, he takes the part of the ultrasonic bath and oil is retained in the bathroom.

As the bathroom has losses by evaporation, additions are made to maintain the level; However, over time the bathroom is filled with mud from the remains of paste polishing and oil; diminishing their ability to clean, so that its complete renovation is necessary. The exhausted bathroom can not be poured or dealt with in a treatment plant chemistry by its high oil content, be a need for its management.

Exhausted after the bath, instead of bringing it to manage, it can be treated by acid fracture technique, which consists of the desemulsionamiento of the oil contained in the sold out degreasing bath based on the fact that the majority of emulsifying agentssuch as soaps and detergents, are less effective in the stabilization of emulsions to low pH's aceite-agua.

Acid break, along with the use of hydrolyzable polyvalent cations such as Fe3 +, can be used not only for the destabilization of emulsions, but in its hydrolysis provides an adsorption effect and drag for part of the Floc forming.

The installation shall form a conical decanter with a key at the base of the decanter for oil output and clarified.

Minimization of the content of heavy metals in waste water

To reduce the concentrations of heavy metals which are not harmful to the environment and limits that conform to standard limits, the precipitation of metals in the form of hydroxide has considered as an alternative.

It proposes an integrated treatment of all previous discharges, (except for the section of pickling/desbarnizado for which is has already described minimization technology), consisting of a conventional physical-chemical treatment.

The flow of water to be treated is the factor that largely determines the dimensions of the installation. Thus, the installation is designed to treat in discontinuous a volume of industrial water of 2,000 litres per load.

The physical-chemical treatment of wastewater is comprised of a series of unit processes used widely in industry and which have proved their effectiveness in a number of operations of water from the surface treatment industry.

In the installation for this cleansing will be treated effluent diluted and concentrates, of acid and basic nature.

The installation consists, essentially, adjustment of pH or neutralization of waste water with the following objectives:

Neutralization should transform heavy metals dissolved in poorly soluble metal hydroxides or basic salts, so that they can be removed from the water.
The final adjustment of pH to adapt it to the values which marks the legislation.

These two objectives cannot be met most of the times of simultaneous and complete form in such a way that it is necessary to reach compromise solutions. If the pH is important deviations from the neutral (pH = 7) organisms present in the water, both vegetable and animal, are severely injured or killed. As a general rule, the deviations towards high pH´s, while they adhere to certain values, are less dangerous than deviations towards low pH´s. For this reason that, taking into account the necessary precipitation of metallic hydroxides, waste water must always be adjusted to a slightly alkaline pH, in the area of pH between 8.5 and 9.0, although legislation allows spills to the network of sewers in up 9.5 of pH value.

The fact that a metal can be precipitated does not imply that the problem of disposal has been fully resolved. The hydroxides of certain heavy metals form colloidal solutions are not settleable or filtrables. This colloidal State can be destabilized by the addition of coagulants, which neutralize surface charge of colloids, allowing his Union in larger settleable Floc.

To facilitate the growth and thickening of the sedimentable Floc, flocculating substance is added. These flocculants are polielectrolitos anionic or cationic high molecular weight, which are composed of long-chain organic with large number of active centers. The long-chain organic act as bridge between different particles forming large agglomerates, easily visible, which go at a reasonable speed.

Decanting is achieved by circulating fluid by a vertical sedimentador where the upward velocity of the effluent is less than the speed of sedimentation of the Floc. At the bottom of the sedimentador sludge, which are periodically evacuated and taken to a depot for storage and espesado of sludge will be deposited. The upper part of the sedimentador does the water already clarified and refined.

In the operation of sludge treatment, increases the percentage by weight of the solids by mechanical dehydration sludge. The reasons why it is interesting to minimize the water content in sludge, are facilitating the manipulation of the mud and, on the other hand, to reduce the waste that has to be evacuated, in volume particularly when it is a toxic and dangerous waste of high management costs.

Minimization of nitrates in wastewater

ara the reduction of the concentration of nitrates of wastewater produced in the rinse of the section of acid pickling to limits that are not detrimental to the environment and which conform to standard limits, has been considered to treat these waters produced and already treated in the facilities described abovewith a team of ion-exchange equipped with selective resin of nitrates.

This treatment involves the removal of the ions nitrate by a team of ion exchange equipped with selective resin of nitrates. This team will remove only this type of ion.

Ion-Exchange team will have to be regenerated on a regular basis in order to achieve the recovery of clearance of these ions by resins. The resulting effluent of the regeneration of the resin will be eliminated through evaporation.

Minimization of waste from the stage of machining

In addition to minimize liquid effluents, recommended to the company a number of good practices during the machining process, in order to reduce further waste to deal with. Some of these measures are given below:

Provided that it is technologically possible, recommended used processes dry, because the waste are more easily recoverable. In case of using wet processes, it will be necessary to treat the effluent prior to discharge.
Possibility to collect the metal powder for later recovery.
All stages are important, so the control and monitoring must be exhaustive, as the stage of mechanical treatments themselves.
Of all the different types of possible mechanical treatments, choosing the first which is technologically applied to our need and, second, that have minimal environmental impact.
Ensure that there are no spots of oil or water, to facilitate the recovery of landfill.

Clarified and waste generated

In the process of debugging is obtained, on the one hand, a non-polluting effluent that can pour freely and on the other hand, you get the following waste:

Mud of purification are managed.
Remains of oil from the acidic breakdown are managed.
Waters of regeneration of the column of ion-exchange which are drying by evaporation in the air in order to reduce the amount of mud to manage.

Also shall be treated as waste that must manage the empty containers of reagents, used rags, and all solid waste.