Challenges and opportunities
Dr Tom Arnot of Bath University looks at the current situation regarding industrial effluent, likely changes to existing legislation and the implications to developing future technologyIn the UK, SMEs and larger companies are facing increasing constraints on the amount and quality of wastewater that can be discharged. This has a large impact on their cost base and restricts their ability to expand or in some cases even to exist at all. Businesses throughout UK industry have continued to place waste minimisation and recycling fairly low down on the agenda but at what cost? Some companies are now seeing wastewater discharge costs increase by a factor of 20 through the implementation of the EU Urban Wastewater Treatment Directive.
The UK government is looking long and hard at how it can meet the requirements of the EU Waste Oil Directive as well as currently implementing the EU Landfill Directive, the EU Nitrates Directive and the EU Water Framework Directive. There is a strong feeling amongst both ministers and industry that the principle of polluter pays needs to be balanced by a workable system that will be easy to implement at ground level. Coupling this with increasing public concern regarding water quality and environmental protection in general, means the issue can no longer be avoided and a number of recent statements serve to reinforce this:
- 1.2Bn people live without access to freshwater, 2.4Bn people lack proper sanitation, and if current trends persist the UN estimates that two-thirds of the world's population will be living with severe water shortages by 2025 - 3rd World Water Conference, Kyoto,
- between 1990 and 2025, the number of people living in urban areas is projected to double to more than 5Bn - UK Energy and Natural Environment Foresight Panel,
- wastewater treatment will become more exacting, creating opportunities for new technologies and management processes - UK Chemicals Foresight Panel,
- the EU Water Framework Directive is the most significant and far-reaching water-related legislation ever - Water UK.
Changes in UK landfill will have a profound impact on the generators of industrial wastewaters.
The following wastes were banned from landfill from July 16, 2002:
- any hazardous waste in liquid form, excluding sludges,
- waste, which under the conditions of the landfill site is potentially corrosive, oxidising, highly flammable or flammable,
- chemical substances arising from research and development or teaching activities which are not identified or which are new and whose effects on man or the environment are not known,
- waste that has been diluted or mixed solely to meet the relevant acceptance criteria for the site.
From the July 16, 2003 there will be:
- no disposal of any waste in liquid form.
From the July 16, 2004:
- all waste being deposited at the site must be pre-treated,
- there will be no co-disposal i.e. no mixing of non-hazardous or inert waste with hazardous waste.
Effectively this legislation will eliminate liquid waste disposal to landfill and enforce the need for some recycling or treatment being applied to most wastes.Further legislation
The Water Framework Directive will have a profound effect on the way in which we handle wastewater entering the natural environment. Estimates produced for the implementation of this directive indicate significant short-term and ongoing costs for SMEs. The UK Energy and Natural Environment Foresight panel report - Stepping Stones to Sustainability, identifies themes such as clearer understanding of regional and local eco- and hydro- systems, reduced water use and cleaner technologies as important over the next 15 years. The UK Chemicals Foresight Panel report - A Chemicals Renaissance, raises concerns over water use and its impact on the chemicals industry, it specifically calls for substantive development of manufacturing processes that generate less waste.
Furthermore the environmental goods and services (EGS) industry in the UK includes many thousands of SMEs, a large proportion of which provide goods and services in the water and wastewater sector. The EGS sector globally is a $500Bn market projected to increase to $700Bn by 2010 and the UK share of this market is estimated at 4.4%. There may therefore be new business opportunities in the development of treatment technologies for industrial effluents.Industry implications
In a recent publication Richard Sheldon of Delft University highlighted the fact that some of the industry sectors traditionally perceived as 'clean' are actually responsible for generating more mass of waste per mass of product than some of the 'dirty' sectors (see Table one).
From this analysis it seems as the scale of production is reduced and the requirement for product purity is increased, the amount of waste generated per product actually increases significantly. One would assume that on this scale the dairy/food/drinks industry comes somewhere ahead of bulk chemicals and that speciality organic chemical manufacturing is similar to pharmaceuticals. It follows that manufacturing companies making more specialised products are going to be the ones hit first by increasing environmental legislation.
The UK Specialised Organic Chemicals Sector Association (SOCSA) has identified the need to treat mixed organic and inorganic liquid wastes as a generic problem. Typical SOCSA member companies are SMEs manufacturing in the UK with a turnover of £5-£60Mpa. They export 65-100% of their output, which consists of many distinct high-value batch-manufactured products, and they need to have a fast flexible response to new business opportunities. Collectively they may need to estimate manufacturing costs for up to 10,000 novel chemicals every year. Estimating the production costs is straightforward but predicting the consequential waste treatment costs is far from easy. This issue is a barrier to commercial sustainability, as when supplying quotations such companies tend to include 'worst case' treatments such as incineration. So how do companies in this and related sectors move forward in the light of tightening environmental legislation?Industrial waste treatment strategies
Before examining individual technology options it is useful to consider more generic questions with regard to the effluent stream, namely:
- Can the components of the waste stream be separated and individually treated or recycled?
- Can the whole organic load of the waste stream be destroyed/oxidised in one step?
- Can separation and destruction/oxidation be integrated to deliver opportunities for raw materials recycling and water reuse?
- Can any components of the waste be processed and recycled for a new purpose?
- Can 'clean and green production' be developed to yield zero waste? Of the five strategies above the first is unfeasible and the second is quite widely used but increasingly unpopular and wasteful of raw materials. The fifth is an ambition for green chemists and proponents of clean/green manufacturing. The third and fourth are pragmatic approaches for the short to medium-term and for the long-term if clean production is never achieved.
Technology options for industrial waste water treatment In theory we have a very wide range of technology options from which to select in order to achieve waste treatment and/or recycling:Physical treatment:
- phase separation - filtration, centrifugation,
- phase transition - distillation, evaporation, drying, physical precipitation,
- phase transfer - extraction, sorption,
- membrane separations - reverse osmosis, nano-, ultra- and micro-filtration.
- incineration and pyrolysis - widely used but increasingly unpopular (800-1,100°C and 1bar) - resulting in the gasification of organics and the production of a small volume of solid ash.
- supercritical wet oxidation - runs under conditions above the critical point for water (500-650°C and 200-1,000bar), providing enhanced solubility of oxygen and organics and thereby attaining complete and rapid oxidation of waste,
- wet air oxidation - organic or inorganic aqueous waste is oxidised at high temperatures (150-300°C) and pressures (10-200bar) in the presence of an oxygen containing gas (usually air).
- advanced wet air oxidation - hydroxyl radicals are generated from sources such as ozone, peroxide, UV light etc to give greater oxidation potential and therefore allow less harsh operating conditions than wet air oxidation.
- the most promising electrochemical destruction processes are known collectively as mediated electrochemical oxidation (<100°C and 1bar). Oxidising metal species such as silver II, cobalt III, cerium IV, and iron III are employed to oxidise the organic waste - there are serious issues relating to metal recycling etc.
- aerobic oxidation - most widely used to oxidise organics and generate biomass sludge (20°C and 1bar) - new technologies are emerging rapidly with regard to membrane bioreactors and extremophile organisms. LI> anaerobic digestion - good for organic sludges and as a first treatment for wastewaters with high COD/BOD content (20-50°C and 1-2bar) - increasing potential with regard to operation at higher temperatures.
While many potential treatment technologies are available it is difficult to assess whether a particular technology, or combination of technologies, will be most appropriate for any given industrial wastewater stream. In trying to make such assessments a number of issues need to be considered:
- technical suitability, maturity, reliability, performance and cost,
- the potential for waste reprocessing and component recycling,
- raw material and service requirements,
- by-product and waste generation - particularly exhaust gases and residual solids,
- safety and environmental considerations,
- process synthesis and technology integration,
- operability and process management.
Ideally we need to build and develop a set of state-of-the-art design protocols that can be applied to the evaluation and integration of potential treatment and/or recycle technologies for industrial effluents. Starting from the industry sectors that are more immediately threatened by the tightening legislation, these protocols and treatment solutions may then be migrated into other manufacturing areas as necessary.
It is ironic the process design considerations that would normally be focussed purely on the manufacturing activity must now also be applied to the resultant waste and wastewater streams, and if this is not done in the near future the manufacturing opportunities themselves may no longer exist. However if we do succeed in the migration of traditional process engineering skills into a more holistic approach to manufacturing and wastewater management we may provide longer sustainability for the current manufacturing base and generate new business opportunities.