Recycling of Lead-Acid Batteries: Perspectives

Lead-acid batteries are used on a mass-scale in all parts of the world for energy storage. Lead-acid batteries contain sulphuric acid and large amounts of lead. The acid is extremely corrosive and is also a good carrier for soluble lead and lead particulate. Lead is a highly toxic metal that produces a range of adverse health impacts particularly among young children.

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Exposure to excessive levels of lead can cause damage to brain and kidney, impair hearing; and lead to numerous other associated problems. On average, each automobile manufactured contains approximately 12 kilograms of lead. Around 96% lead is used in the common lead-acid battery, while the remaining 4% in other applications including wheel balance weights, protective coatings and vibration dampers.

Recycling Perspectives

Recycling of Lead-Acid Batteries is a profitable business, albeit dangerous, in developing countries. Many developing countries buy used lead-acid batteries (also known as ULABs) from industrialized countries (and Middle East) in bulk in order to extract lead. ULAB recycling occurs in almost every city in the developing world where ULAB recycling and smelting operations are often located in densely populated urban areas with hardly any pollution control and safety measures for workers.

Usually ULAB recycling operations release lead-contaminated waste into the environment and natural ecosystems.  Infact, Blacksmith Institute estimates that over 12 million people are affected by lead contamination from processing of Used Lead Acid Batteries in the developing world, with South America, South Asia and Africa being the most affected regions.

Associated Problems

The problems associated with recycling of ULABs are well-documented and recognized by the industry and the Basel Convention Secretariat. As much of the informal ULAB recycling is small-scale and difficult to regulate or control, progress is possible only through cleanup, outreach, policy, and education.

For example, Blacksmith’s Lead Poisoning and Car Batteries Project is currently active in eight countries, including Senegal, the Dominican Republic, India, and the Philippines. The Project aims to end widespread lead poisoning from the improper recycling of ULABs, and consists of several different strategies and programs, with the most important priority being the health of children in the surrounding communities.

Lead poisoning, from improper recycling of used batteries, impacts tens of millions of people worldwide.

Lead poisoning, from improper recycling of used batteries, impacts tens of millions of people worldwide.

There is no effective means of tracking shipments of used lead-acid batteries from foreign exporters to recycling plants in developing world which makes it difficult to trace ULABs going to unauthorized or inadequate facilities.

The Way Forward

An effective method to reduce the hazards posed by trans-boundary movements of ULABs is to encourage companies that generate used lead batteries to voluntarily stop exporting lead batteries to developing countries. These types of voluntary restrictions on transboundary shipments can help pressure companies involved in recycling lead batteries in developing to improve their environmental performance. It may also help encourage policy makers to close the gaps in both regulations and enforcement capacity.

Another interesting way is to encourage regeneration of lead-acid batteries which can prolong its life significantly. The advantage of battery regeneration over regular recycling is the reduced carbon footprint incurred by mitigating the collecting, packing, shipping and smelting of millions of tonnes of batteries and their cases. Most importantly, it takes about 25kWh of energy to remake a 15Kg, 12V 70Ah battery and just 2.1KWh to regenerate it electronically.

Biological Desulphurization of Biogas

The most valuable component of biogas is methane (CH4) which typically makes up 60%, with the balance being carbon dioxide (CO2) and small percentages of other gases. However, biogas also contain significant amount of hydrogen sulfide (H2S) gas which needs to be stripped off due to its highly corrosive nature. Hydrogen sulfide is oxidized into sulfur dioxide which dissolves as sulfuric acid. Sulphuric acid, even in trace amounts, can make a solution extremely acidic. Extremely acidic electrolytes dissolve metals rapidly and speed up the corrosion process.

The corrosive nature of H2S has the potential to destroy expensive biogas processing equipment. Even if there is no oxygen present, biogas can corrode metal. Hydrogen sulphide can become its own electrolyte and absorb directly onto the metal to form corrosion. If the hydrogen sulphide concentration is very low, the corrosion will be slow but will still occur due to the presence of carbon dioxide.

Biogas_Cleanup-H2S

The obvious solution is the use of a biogas cleanup process whereby contaminants in the raw biogas stream are absorbed or scrubbed. Desulphurization of biogas can be performed by biological as well as chemical methods. Biological treatment of hydrogen sulphide typically involves passing the biogas through biologically active media. These treatments may include open bed soil filters, biofilters, fixed film bioscrubbers, suspended growth bioscrubbers and fluidized bed bioreactors.

Biological Desulphurization

The simplest method of desulphurization is the addition of oxygen or air directly into the digester or in a storage tank serving at the same time as gas holder. Thiobacilli are ubiquitous and thus systems do not require inoculation. They grow on the surface of the digestate, which offers the necessary micro-aerophilic surface and at the same time the necessary nutrients. They form yellow clusters of sulphur. Depending on the temperature, the reaction time, the amount and place of the air added the hydrogen sulphide concentration can be reduced by 95 % to less than 50 ppm.

Most of the sulphide oxidising micro-organisms belong to the family of Thiobacillus. For the microbiological oxidation of sulphide it is essential to add stoichiometric amounts of oxygen to the biogas. Depending on the concentration of hydrogen sulphide this corresponds to 2 to 6 % air in biogas. Measures of safety have to be taken to avoid overdosing of air in case of pump failures.

Biofiltration

Biofiltration is one of the most promising clean technologies for reducing emissions of malodorous gases and other pollutants into the atmosphere. In a biofiltration system, the gas stream is passed through a packed bed on which pollutant-degrading microbes are immobilized as biofilm. A biological filter combines water scrubbing and biological desulfurization.

Biogas and the separated digestate meet in a counter-current flow in a filter bed. The biogas is mixed with 4% to 6% air before entry into the filter bed. The filter media offer the required surface area for scrubbing, as well as for the attachment of the desulphurizing microorganisms. Microorganisms in the biofilm convert the absorbed H2S into elemental sulphur by metabolic activity. Oxygen is the key parameter that controls the level of oxidation.

The capital costs for biological treatment of biogas are moderate and operational costs are low. This technology is widely available worldwide. However, it may be noted that the biological system is capable to remove even very high amounts of hydrogen sulphide from the biogas but its adaptability to fluctuating hydrogen sulphide contents is not yet proven.