Question

Choose an environmentally unsustainable industrial practice. Briefly define and explain your chosen unsustainable industrial practice. Then, use three green engineering principles to mitigate the effects of this practice on the environment. For each green engineering principle, you should articulate how each principle can mitigate the environmental effects of the chosen unsustainable practice.

Principles:

1. Designers need to strive to ensure that all material and energy inputs and outputs are as inherently non-hazardous as possible

2. It is better to prevent waste than to treat or clean up waste after it is formed

3. Separation and purification operations should be a component of the design framework

4. System components should be designed to maximise mass, energy and temporal efficiency

5. System components should be output pulled rather than input pushed through the use of energy and materials

6. Embedded entropy and complexity must be viewed as an investment when making design choices on recycle, reuse or beneficial disposition

7. Targeted durability, not immortality, should be a design goal

8. Design for unnecessary capacity or capability should be considered a design flaw. Including ‘one fits all’ solutions

9. Multi-component products should strive for material unification to promote disassemble and value retention (minimise material diversity)

10. Design of processes and systems must include integration and interconnectivity with available energy and material flows

11. Performance metrics include designing for performance in commercial ‘after-life’

12. Design should be based on renewable and readily available inputs

Answer 1

PAPER AND PULP INDUSTRY SEWAGE DUMBING

Sewage emerging from a pulp and paper industry contains various polluting constituents because in the processes involved in pulp and paper industry various chemicals are used. As such treatment of the sewage is necessary prior to its disposal.Processes Involved in Pulp and Paper Industry:

(a) Raw Material

The raw materials are-

i. Cellulosic and

ii. Non-cellulosic.

i. Cellulosic Raw Materials:

Bamboo is the principal cellulosic raw material. However, wood (hard or soft) is now being increasingly, used. Straw, mainly rice and wheat; grass; jute sticks; sunn hemp; old ropes; hessian; cotton linters and rags; bagasse; and waste paper are also used as raw material in small paper mills and also for specialty paper in bigger mills.

ii. Non-Cellulosic Raw Materials (Chemicals):

These are – caustic soda, sodium sulphate, sodium sulphite, sulphur, bisulphites of calcium and magnesium, lime, limestone, chlorine, chlorine dioxide, hypochlorites of sodium and calcium, hydrogen peroxide, sodium peroxide, china clay, talc, rosin, starch, alum, glue, dyes and gums.

Sewage is contributed from different sections of the pulp and paper industry as indicated below:

(a) Raw Material Preparation Section (Chipper House):

The effluent from this section results from washing, cleaning, barking and chipping of the cellulosic raw materials.

(b) Pulp Mill:

The effluent from pulp mill consists of:

(i) The spent liquor known as Black Liquor (BL);

(ii) Effluents from brown stock washers, chlorination, caustic extraction and hypochlorite bleaching.

(iii) Chemical recovery process;

(iv) Spills and leakages; and

(v) Wash water from bleach liquor and chemical preparation plants.

(c) Paper Machines:

Stock preparation and paper machine effluents which include excess white drainage

(d) Caustic-Chlorine Plant:

The effluent from caustic-chlorine plant consists of-

(i) The sludges from brine purification and filtration and caustic filtration;

(ii) Condensates from vacuum dechlorinators and chlorine system;

(iii) Condensate from hydrogen cooling system; and

(iv) Other effluents from cell room and floor washes.

Quantity:

The quantity of sewage produced from a pulp and paper industry depends on the total production, the types of paper made, water supply and on the practices adopted for reuse of effluents within the mill operations. As such the quantity of sewage considerably differs from mill to mill, and it may vary from about 200 to 350 m3 per tonne of paper produced.

SOLUTION USING SUSTAINABLE PRINCIPLES

12. Design should be based on renewable and readily available inputs.

The main disadvantage of this industry is that they use trees as input which result in deforestation. This part can be made sustainable by adopting the 12th principle of design for sustainabilitysustainability i.e by using recycled paper and ready made units like imported pulp.

Most of the current paper production can be made by the recycled paper and imported pulps. Such processes have advantages from environmental point of view since they require 40-50% less amount of water than the chemical pulping process.

1. Designers need to strive to ensure that all material and energy inputs and outputs are as inherently non-hazardous as possible.

The inputs of paper and pulp industry is primarily bamboo and wood. It also includes chemicals for the further processes. But the effluents from the waste generated can be solved sustainably by using proper treatments so that they become unhazardous.

Pulp and paper mill effluents can be treated either by physicochemical, biological method or their combination.

Biological treatment can further be classified as anaerobic and aerobic. Fungal treatment of colored effluent from pulp and paper mills has also shown satisfactory results.

Even significant decrease in pollution load and wastewater volume have been reported because of changes in mills’ internal process and managerial measures. Physicochemical treatment processes remove suspended solids, colors and even BOD and COD by screening, co- agulation, flocculation, sedimentation, flotation, adsorption etc. Chemical precipitation can be used for removal of heavy metals and dissolved solids.In biological treatment, metabolic function of microorganisms are used to remove BOD, COD and capture suspended and nonsettleable colloidal solids either in presence (aerobic) or absence (anaerobic) of oxygen.

Combination of the above two processes are often employed. In most pulp and paper mills, biological treatment is followed by physicochemical process. More advanced ter- tiary treatment methods are also often employed.

4. System components should be designed to maximise mass, energy and temporal efficiency

Material efficiency is part of sustainable development, and taking it into account is now more important than ever due to the growing scarcity of natural resources. Material efficiency covers the minimization of raw materials used in the production process, selection of the most economical raw materials possible, and the reduction and recycling of waste to minimize the amount of unutilized material.

The raw material is a major cost factor for pulp and paper mills since raw materials represent about 50% of total operating costs. It also provides an opportunity to boost profitability by minimizing the amount of waste, and related costs. By minimizing waste and recycling waste material, producers are able to meet global agreements and environmental protection goals, and thus help to promote sustainable.

Pulp and paper mills can save raw material costs by minimizing the use of expensive raw materials (e.g. bulk-saving solutions at the press and drying sections and calenders) and reducing the consumption of chemicals (e.g. OptiCell flotation unit).

Maximizing the lifetime of consumables through optimized design (e.g. screen basket,coater blades) and reusing reconditioned equipment (e.g. refiner reconditioning and refiner exchange program) helps to cut equipment costs. Recycling such consumables as doctor blades and rod beds also save money.