Gulf Construction Online - Saudi firm launches neutralisation plant

Water Technology

Sew's new neutralisation plant includes a reactor tank with acid day tank and solid settling tank

Saudi firm launches neutralisation plant

A neutralisation plant has begun operations in the Eastern Province of Saudi Arabia. Saudi Company for Environmental Works (Sew) elaborates on the plant and the waste treatment process it employs.

01 September 2003

Saudi Company for Environmental Works (Sew) launched operations at its newly-built neutralisation plant at the end of last month.

The plant was developed as part of a comprehensive programme to improve and upgrade its treatment and disposal facilities.
The plant at Sew's Eastern Province waste treatment facility will allow it to thoroughly treat and dispose of waste acids and bases, as well as other amenable wastes, using neutralisation, precipitation and oxidation/reduction reactions, according to operations manager Hugh Van Noordwyk.
The rapid industrialisation of Saudi Arabia since the 70s has, unfortunately, also brought about the pollution of the environment. Industries have slowly realised the value and importance of setting up proper waste management processes, to tackle problems of pollution, he says.
One of the fundamental and most common technologies available for the treatment of hazardous waste is neutralisation, according to Noordwyk.
'It involves the addition of an acid or a base to the waste to adjust its pH upward or downward, as required,' he explains. 'It also serves as a form of pretreatment for optimisation of performance of pH-sensitive processes or for minimisation of corrosion in more sophisticated physical/chemical treatment.
'The process of neutralisation uses bases such as lime (CaO), calcium hydroxide (Ca(OH)2), caustic (NaOH), soda ash (Na2CO3) and ammonium hydroxide (NH4OH). Acids commonly used include sulphuric acid (H2SO4), hydrochloric acid (HCl) and nitric acid (HNO3).
'Closely related to neutralisation are reactions involving precipitation and oxidation/ reduction. Precipitation involves a physical/chemical process in which a dissolved metal is solidified for removal. Chemical equilibrium relationships between soluble substances are generally altered by the addition of chemicals such as lime and sodium sulphate.
'Oxidation/reduction reactions involve the chemical transformation of reactants in which the oxidation state of one reactant is raised while the other is lowered. The process eliminates or reduces the toxicity of many organic compounds and heavy metals.'
Sew's new plant will neutralise aqueous, inorganic acids and bases, perform precipitation reactions and accomplish oxidation/reduction reactions.
The neutralisation facility, which has a throughput of approximately 100 cu m per eight-hour shift, is being operated on a batch basis after carefully monitoring the reactants. To ensure this, the plant has control and shutdown valves, flow meters and a pH/ORP (oxidation reduction potential) meter. Other key components of the plant include caustic storage tanks, an acid day tank, a reaction tank with mixer, a solids settling tank, a solids drying area, pumps and controls.
Elaborating on the process used , Noordwyk says: 'Initially, waste acid is pumped into the acid day tank from the storage lagoon, which is lined with double membrane high-density polyethylene liners incorporating a leakage collection system to prevent subsurface contamination. The waste acid is then pumped into the reaction tank to which caustic is pumped at a predetermined rate from the caustic storage tanks. The tank mixer is adjusted to an optimal speed to ensure complete mixing of the two reactants. The pH and ORP of the mixture is then monitored until a neutral pH reading (approximately 7) and an ORP of near zero have been attained, at which time the neutralisation is deemed to be complete.
'Once neutralised, the resultant water of neutralisation is sent to a settling tank where the majority of the solids will settle down. These solids are then transferred to the solids drying pad. Once dried, the solids are collected and placed in drums. The collected solids undergo TCLP testing and are eventually disposed of in the Class I landfill or Class II landfill at Sew's waste disposal facility depending on the results of the tests.
'Water is pumped from the settling tank to evaporation ponds where it evaporates. Residue, which collects on the bottom of the ponds, is eventually allowed to dry, and will be tested and properly disposed of in an appropriate landfill.
The plant incorporates various aspects that ensure the health and safety of the personnel. The plant has spill control (epoxy-lined floors and walls, drains and sumps), an emergency shower, emergency eyewash, first aid kit, fire extinguishers and other relevant safety equipment. Plant staff are trained in aspects of operation and safety, and are equipped with protective equipment.