The directive on integrated pollution prevention and control has prompted a swarm of interest in identifying BATs - best available techniques

IPPC steps up to BAT

The first IC reactor installed in a paper industry application at Sical's mill in France

BATs come into play

The pulp and paper industry is listed under a sixth category called "other industries", along with textiles, tanneries, intensive pig-rearing, etc. All pulp mills are subject to the IPPC regulations, but only paper mills with a capacity above 20 tons/day will be affected. The implication is that the environmental impact of all mills below this size is trivial and therefore not significant, which may or not be true.

Unlike the UK's integrated pollution control (IPC) legislation on which IPPC was modeled, the size of a plant is the only test for triviality. But at least this admittedly simplistic criterion means that the industry does not have to underpin the financial performance of the EU's analytical laboratories for months while the very low and usually non-detectable concentration of various herbicides in its wastewaters is measured.

Through IPPC, the intention is to prevent or, where this is not practicable, to reduce emissions to air, water and land. In this way, the system is designed to achieve a high level of protection of the whole environment. Under the terms of the regime, licensed installations must be operated in such a way as to meet six prime objectives:

• the use of best available techniques (BAT) to prevent pollution

   

• no significant pollution is caused

   

• waste minimization and the recovery of unavoidable waste

   

• the efficient use of energy

   

• the prevention of accidental releases

   

• remediation of the site to its original state on closure of the plant.

   

The integrated nature of the directive refers to the potential for all materials leaving the mill in a waste stream to be re-distributed in some way during waste treatment. For example, materials in wastewater often end up either as part of a solid waste deposited on land or a gaseous output to atmosphere.

The directive seeks to ensure that such cross-media effects do not run counter to one another by placing emphasis on protecting the whole environment, but it is not clear how this will be achieved in practice. This aspect is certainly one of the more difficult facets of the UK's IPC system, but this did have the advantage of a protocol for establishing the Best Practicable Environmental Option (BPEO) in such circumstances. The IPPC directive contains no such concept.

In order to facilitate the even-handed application of IPPC across the EU's supposed level playing field, the directive provides for an exchange of information on BATs. Indeed, in 1997 an IPPC bureau was set up in Sevilla in Spain for this purpose. The primary activity of this unit to date has been the preparation of BAT reference (BREF) documents, the first of which is on the pulp and paper sector. This was published as a draft for comment in August last year and is now in the course of being revised in the light of comments received during consultation with industry. It should be published in its final form later this year.

In the draft BREF document, the industry is broken down into five different unit processes - kraft pulping, sulfite pulping, mechanical pulping, processing of recovered paper and papermaking. Within each section, there is an overview of the operations involved and a discussion of various candidate BATs before defining BAT in terms of various process options and emission levels of various parameters. The emission parameters are specified in the form of kg substance/ton of pulp or paper. The list comprises:

• BOD, COD, TSS, AOX, total phosphorous, total nitrogen and flow (m3/ton) for the wastewater

   

• particulates, SO2 and NOx (plus TRS at kraft mills) for emissions to air

   

• non-hazardous solid waste to landfill.

   

The treatment techniques are relatively well-established. The major role usually goes to aerobic biological treatment processes, plus anaerobic pre-treatment in its proven niches, eg on sulfite evaporator condensates and wastewaters from packaging mills based on non-deinked recovered paper. The only tertiary treatment process considered as BAT is the use of chemical precipitation for the removal of phosphate and residual organics at chemical pulp mills. But this was rejected as a current BAT due to limited full-scale use to date.

Bio-BATs for wastewaters

Anaerobic treatment is now a well-established technology. It is most often encountered in its most common guise of the popular upflow anaerobic sludge blanket (UASB), but it is also found in somewhat rarer contact reactors. One of the advantages of anaerobic versus aerobic treatment has always been compactness and small footprint, as the reactor size is not dictated by the need to dissolve oxygen in the liquor.

The most compact anaerobic reactors are the few genuine fluidized bed reactors, which achieve excellent mixing and mass transfer by recirculation of the treated wastewater. Compared to typical loadings of about 2 kg COD per m3 reactor volume per day for aerobic activated sludge plants, the lowest rate anaerobic plants achieve about twice this output and the traditional UASB reactors can handle up to about 15 kg COD/m3.day.

Several UASB systems suppliers have developed more intensive, high-rate UASB reactors, so that the application of anaerobic treatment could be extended to weaker, cooler wastewaters. Initially, these reactors were used in the food and drinks industry, but several have been installed at paper mills in the last few years.

The main two designs are the Biobed system from Biothane and the IC (Internal Circulation) reactor from Paques based in The Netherlands. The Dutch company has installed over half the total number of anaerobic treatment plants in the pulp and paper sector. The IC reactor has a tall, slender design. It has an expanded granular bed at the bottom of the unit with a gas-lift riser pipe taking sludge/gas to the top. The sludge returns to the base via a downer pipe. The first IC reactor in the paper industry was installed in 1996 at the Sical mill in France, which makes corrugating medium. The wastewater temperature is only 23C compared to the 30-35C normally required, but it achieves a COD removal of about 70% at an average loading of 20 kg COD/m3.day.

Another way to increase the loading is by thermophilic treatment at 50-60C. Again, an IC reactor is the first plant of this type to be utilized and one is being installed this year at a Dutch board mill that already has no wastewater discharge.

Membrane treatment (ultrafiltration) is mentioned in the context of the recovery of coating solids from segregated coating wastewaters and the internal treatment of process waters at mills using virgin pulp. Both applications are concluded to be BAT, but not for all mills. One of the few mills using ultrafiltration within the paper machine system is Metsä-Serla's Kirkniemi mill, but there are now quite a few coating applications of ultrafiltration. (For more details on Kirkniemi, see PPI, June 1997, pages 43-46.)

ZED = BAT?

The only situation where zero effluent discharge (ZED) is considered to be BAT is the well-known and proven use of evaporation/incineration at non-integrated CTMP (chemi-thermomechanical pulp) mills. Within the non-deinked recycled fiber sector, the partial re-use of bio-treated effluent is defined as BAT, but the degree of closure is left to individual mills.

Two European recycled mills have achieved ZED through anaerobic/aerobic treatment of circuit waters, but most ZED mills in the USA have reached this position by simpler means. However, there are exceptions and one a good example is the ZED recycled linerboard mill run by McKinley Paper in New Mexico.

The limited nature of water supplies in this location provides the ultimate motivation for a mill to close up its water system and McKinley has achieved this by incorporating both conventional techniques and more novel ideas.

As can be seen from the simple circuit diagram in Figure 1, the mill is relatively closed upstream of the wastewater treatment system, using only about 2 m3/ton of "fresh water". This is in fact a mixture of low conductivity water supplied from an adjacent power station and the final waters regenerated from the wastewater treatment system. The conventional part of the water reclamation system involves primary flotation and secondary aerobic bio-treatment, which removes about 90% of the incoming COD (3-5 g/l). The sludges from the first two stages comprise most of the pressed cake, leaving the site for use in composting, either as a fuel or for landfilling.

The more novel part of the plant starts with not one, but two different types of membrane filtration. The tertiary stage uses the simplest type of membrane - micro-filtration - to remove fine, colloidal solids. This process is used by a few other mills in this position in the treatment train (albeit not within a ZED system), but the quaternary stage uses the most efficient type of membrane - reverse osmosis.

Using this technique concentrates most of the remaining dissolved solids (largely salts), which are then concentrated further in a quintinary evaporation stage using the technique of mechanical vapor recompression (MVR). The RO permeate and MVR distillate are then recycled to the mill's fresh water tank to close the loop. These final stages are able to stabilize the quality of the mill's whitewater at about 5 mS/cm conductivity and 1 g/l chloride - levels that are still quite high, but which can be reached at other mills with quite open water systems.

A common feature of several of the water management BATs within the draft IPPC BREF is the separation of water circuits, particularly between pulping/bleaching activities and papermaking. This process element is usually achieved by thickening the pulp suspension to the maximum extent possible. Despite being a fairly low level technology, this is very effective at keeping the dissolved solids away from the paper machine where they generally only cause problems.

For most mills using direct-entry recovered paper, the fiber is the main source of dissolved substances, which may be as high as 50 kg COD/ton in some instances. The concept outlined above could easily be utilized at such mills, particularly where a disperging stage is present as this is usually preceded by a thickener. At other mills such as woodfree printings/writing plants using virgin pulp, the broke is likely to be the main source of dissolved substances, largely due to the addition of starches at the size press. In this case, thickening would then be applied just to the re-pulped broke, not to the incoming pulp.

How this might look in these two situations is illustrated in Figure 2 where the filtrate is shown as being bio-treated internally to remove the bulk of the (organic) dissolved solids. This internal use of bio-treatment is not essential, as the filtrate could simply be routed to an external treatment system. The results of applying this simple technique to broke is shown in Figure 3, assuming that the filtrate is routed externally or that the removal of total dissolved solids (TDS) on bio-treatment is 100%. Thickening the broke to just 15% lowers the TDS concentration at the machine wet end by two thirds, but what suffers is naturally the dissolved material's retention.

In this moderately open/closed water system, the total retention of TDS was about 25% without broke thickening, but this drops to below 10% on thickening. Doing anything that deliberately lowers the overall retention would seem to go against the principles of IPPC. But this concept could well be considered BAT if bio-treatment recovers something of value from the TDS (eg methane in the obvious case of an anaerobic process) and if it allows greater closure of the machine's water system.

Sludge BATs

Waste minimization is a key objective within IPPC. If we define waste as anything that doesn't end up in the product, then virtually all the internal BATs have a waste minimization dimension, for example:

• closed screening and improved washing at kraft mills

   

• optimal reject treatment at mechanical pulp mills

   

• optimized stock preparation at mills using direct-entry recovered paper

   

• reduced fiber and filler losses in papermaking

   

• ultrafiltration of coating wastewaters.

   

If we define waste somewhat more broadly as anything that doesn't end up being used beneficially in some way, then this brings in a number of BATs that recover something of value from primary waste. Unsurprisingly, the main technique that crops up in several places in the draft BREF is incineration, with energy recovery as applied to bark, rejects and sludges. The incineration of rejects from recovered paper processing is the newest of these with still only a few full-scale plants, particularly at non-deinked mills.

What is claimed to be the world's largest sludge/rejects incinerator is due to start up this year at the expanded Norske Skog newsprint mill at Golbey in France. This bubbling fluidized bed unit from Kvaerner will burn 400 tons/day of dry solids from bark, deinking sludge and rejects.

Taking an average rejects content in recovered paper of 5%, a large non-deinked mill will only produce about 50 tons/day dry rejects. This is enough to run a small incinerator, but the installation and operating costs are high compared to the larger units suitable for deinking mills.

One solution for smaller mills that is practiced in the Netherlands is to club together with other nearby mills and build a jointly-owned incinerator. A research program at CTP in France has shown that rejects can be incinerated on their own and achieve high emission standards (or in a municipal waste incinerator at a 20% level) with no problems.

Many existing boilers that use solid fuel (eg bark, coal and peat) have been modified to burn sludges. In addition, a few chemical pulp mills (both kraft and sulfite) incorporate bio-sludges into the pulping liquor for burning. In the USA, one kraft mill is also modifying an existing recovery boiler to a fluidized bed design in order to incinerate bark, other wood wastes, primary wastewater sludges and tires.

One method of beneficial sludge re-use that is not covered in the draft BREF is a technique that has seen its popularity increase steadily through the 1990s - namely, land spreading or land application. Any technique of simply placing waste on the ground, whether it be landfill or landspread, has the potential to cause problems from leachates. The leachates may contain substances in the waste or those produced by biological activity. The bio-activity in landspread should be aerobic and create harmless products, whereas the anaerobic activity more common in landfills is responsible both for its potential benefits (methane gas as an energy source) and its problems (strong leachates and odors).

Landspreading is widespread in North America. For example, about 20% of sludges followed this route in the province of Quebec in 1997. In the UK, nearly all sludges were landfilled 10 years ago. Today, only about one third of the total volume goes to landfill, while another 20% is incinerated and the rest (about 45%) is landspread. The latter route is particularly popular for deinked sludges, where about half is landspread and less than 30% landfilled.

Landspread is popular because it is cheaper than landfill, but it also places responsibilities and costs on the mill in terms of sludge/soil/crop monitoring and demonstrating that the operation is beneficial and without harm. In response to what is likely to be stronger regulation, the UK Paper Federation has issued a Code of Practice to help mills ensure that the operation is sustainable and managed to the highest practicable standards.

Batting for the future

IPPC BATs are not fixed forever. The relevant authorities in each country have to follow or be informed of BAT developments and the information gained is exchanged between member states in the EU. There is no organized EU research to develop and demonstrate new BATs, but ongoing research programs can be utilized.

Since 1971, there has been a program on Cooperation in Science & Technology (COST), which is administered by the European Commission, but with membership extending to many non-EU countries. Last year, a new COST initiative (E14) got under way under the title "Towards Zero Liquid Effluent (ZLE) in Papermaking".

The estimated cost of this substantial program is ECU 30 million (at 1997 prices) and the main objective is to provide industry with a means to substantially reduce the cost of water conservation in papermaking. This is something that fits in with IPPC and many of the draft BATs. The proposed COST program consists of two strands - fundamental research and applied research, demonstration and management. The types of activities included under the scheme range from workshops, seminars and conferences (the first was held in the Netherlands two months ago); exchanges of information and experts; and collaboration projects between universities, institutes and paper companies.