An Environmental Chemistry Curriculum Using Case Studies Vincent K.W. Cheng Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong

Some time ago, I was given a teaching assignment on the methods of removing industrial pollutants. The program involved lecturing on applied chemistry to a large class of final-year students. Occasionally practicing consultants were invited to share their experience with us. The ohjec- tives of the course were

(1) to outline the serious pollution problem in Hong Kong, an overcrowded and fast-growing industrial city;

(2) to provide a description of the methods available.

Our students were unhappy with the need to memorize the large quantity of unorganized factual materials. The teaching materials were mostly from standard textbooks published in the United States. We also recognized the learning difficulty of our students. They are rather passive and most of them have forgotten their basic physical chem- istry. They could not respond with a simple question on the feasibility of these alternatives, particularly in the local context; however, a positive feedback to the course materi- als is their appreciation of the simplicity of the chemistry involved and some of these methods actually involve some novelty ( I ) .

We felt that further improvement was necessary to make the program interesting and intellectually challenging to the students. Applied science involves rather simple scien- tific knowledge but its intellectual challenge is decision making, i.e., to establish the criteria of the effective use of the alternatives as determined by the cost of the chemistry, the design, operation, and maintenance of equipment etc.

We proposed the use of case study to improve the cur- riculum. Because we have large classes, seminar sessions in the sense given earlier (2) may not be appropriate. Case study is not a new concept in teaching. I t has been success- fully used in the teaching of business management (3); thus, its potential in environmental management is not a surprise. I t also finds its way into synthetic chemistry (4) , history and philosophy of science (51, and artificial intelli- gence (6). A case study is simply a description of a real life occurrence that calls for decisions and actions. I t provides a n opportunity to study methods that did or did not work in a particular set of circumstances. In its simplest context, a numerical example and related exercise properly de- signed can be regarded a s a starting point. The student is presented with the facts and opinions expressed in the case. We will assess his or her written or verbal analysis of the information given; i.e., the identification of problems and decisions on feasible solutions. I t may require team work; thus, students will have the opportunity to develop such skill.

The Revised Curriculum We expanded our initial learning objectives to include a

quantitative statement of the serious pollution problem in Hong Kong, e.g., the amount and types of pollutants pro- duced by industry and their environmental impact. De- spite the availability of a number of known methods to re- move industrial pollutants, the pollution problem remains unresolved. The new objective of the curriculum was to as- sess the feasihility of these methods in the local context. In Hong Kong, we have to deal with pollutants produced in large quantities by small factories in high rise apartments,

and their removal pose extra difficulties. Low cost, com- pact, chemically efficient, on-line equipment installed in individual factories would be a desirable solution. Thus, we need to develop the skill to evaluate the existing solu- tions or their modifications to the problems.

The Course Contents Our teaching program covered a number of industries

that had serious environmental imoacts. For each t v ~ e of . . industrv, I ident~fied a number ol'porenrially frasihlr trrat- ment methods. In the C:IS(! studirs. 110th thtr vhsslcal chcm- istry involved rmostly t ~ x t t ~ o ~ k m;~telials hi thc factore rh:~t affict thr ovcrarlna cost of each method were consid- ered. In this coimunic&on, I illustrate the case study ap- proach with the electroplating industry.

From our survey of electroplating factories in Hong Kong, the most common process involves the plating of nickel, chromium, and copper. The effluent discharged is rinse water containing cyanide, Cr(VI), Cu(II), and Ni(I1) ions a t a wide range of concentrations (less than 6 m m o n for Ni and 0.5 mmoYL for Cu). From the known amount and tvnes of discharee. we can auantifv the cost of the

" A - . treatment processes involved.

The scale of these operations is measured in terms of the number of workers employed, size of the factory, and the volume of waste water discharged. (See Table 1.)

Table 1. Summary of Scale of Operation in Hong Kong Electroplating Factories

Size of Factory Staff Number Facto Area Volume of % (m ) Waste Water (m3/day)

small <20 20-80 3-5 medium c50 150-250 1 W O

large >50 300-1 000 5 M O

The first problem to consider was the type of reactor suited for the scale of overation. For a small factorv. a batch reactor is recommended and this decision is madebn economic grounds; i.e., the operation cost, the quantity of effluent produced each day and the size of the reactor. However. this oroblem is a n o~ t iona l tooic because the en- gineering issues to he considered are-non-chemistry re- lated. When the operation is sealed up to a medium or large size factory, a continuous flow reactor may he desir- able.

The important problem on hand was to evaluate the most suitable chemical process in terms of the cost and the effectiveness of the chemistry. The following nonchemistry actors were considered:

1. quantity, availability, and the cost of chemicals, 2. transportation cast of further waste to be disposed; e.g.,

precipitation. 3. incentives far the investment of equipment, given the pre-

sent state of our environmental protection ordinance and its enforcement.

4. reaction time taken. This factor may rule out the biatech- nology of the day

5. safety and training of operator for the equipment.

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6. available space far pollution control equipment

In the case study, initial specific instructions on how to approach the analysis may enable students to appreciate the way to form and evaluate opinions. We began with sim- ple numerical examples to deal with one or two simple con- cepts of physical chemistry, for example, the relationship between precipitation, equilibrium constant, and the ac- cepted concentration limit of wastewater.

I also outlined the alternative chemical processes, and I chose feasible methods such a s ion-exchange reaeent and the prwipltat~on of'hrii\?. rnt:tnls ns hydrowdes or s u l l i d ~ s . Several reactions for thc dcstrurtion ol'rvnnidt~ In oxidn- tion with chlorine, ozone, and sodium hypochlorite were considered. Sodium metahisulphite, NazSzO6, is the pre- ferred reductant for Cr(VIi over SOz and FeS04 and scrap iron. Precipitation appears to be effectivecheap and fast. I t is well accepted locally and overseas (7) where further waste (precipitate) disposal is feasible. The equilibrium constant of sulfide precipitation by the addition of sodium sulfide is higher that that of hydroxide. I t would he pre- ferred if the environmental ordinance is restrictive and the cost is sufficiently low.

Whether these waste waters should be mixed and treated simultaneously would be a n appropriate question for the reactor design. The oxidation of cyanide by sodium hypochlorite gives cyanate, hut i t may be converted back to cvanide hv the reductant in the chromium reduction. Hence the recommended treatment system contains sepa- rate stages of cyanide removal, hexavalent chromium re- duction, and heavy metal precipitation. The cost of equip- ment for waste treatment base on these processes is given is Table 2.

Ion exchange is a n attractive means of removal and, most importa&ly, recycling of heavy metals. In addition to the chemical aspects of ion exchange, we covered the eco- nomic advantage and disadvantage of ion exchange in terms of the exchange capacity, cost of equipment, mainte- nance and oneration. We cited a case involving a small factory with equipment for nickel recov- ery. The cost of the equipment is about US $12,000 and the ion-ex- change resin (weak acid type) is developed and produced jointly by the Hong Kong Productivity Council and the NanKai Univer- sity in China. The cost of equip- ment without the recovery part (ion exchange only) is 113 of the full cost and central facility for regeneration a t the Hong Kong Productivity Council is available a t a price (US $100 per visit). Be- cause the recovery operation pro- duces nickel solution with a nar- row range of concentration and p H for reuse, a n experienced andlor academically qualified technical staff is required. That will undoubtedly add extra cost to t h e operation. Recovery of nickel is made once a week, and the solution can he reused with- out further processing. The natu- ral extension of the case study would be the generalization of the cost issue to medium and large factories of which we do not have any information a t present. With the increase in the volume

of waste water produced, we need to increase the fre- quency of nickel recovery-recycle operation per week.

We also highlighted the need for research and develop- ment work on ion exchange. Recovery of copper is not suc- cessful and further work to solve this problem is on going. Students should appreciate that precipitation because the recommended answer is simolv a less exoensive choice. . " The preparation of low-cost ion-exchange resin is a desir- able research strategy. Such novel cases (1) would enable students to appreciate the importance of research and de- velopment in this field. The exoeriment we ~reviouslv re- portkd (I) has its potential in the teaching1~boratory.-

The final issue to consider was the transport of waste disposal of precipitate and recycling of exhausted ion-ex- change resin. Depending on the distance travelled (20-30 km), the cost of transport is between US $15 and 25 per trip. The economic and transportation factors are impor- tant issues in Hong Kong because most factories are inside multi-story apartment buildings with small floor area and limited loading zone for motor vehicles. Limited landfills available for disposal of precipitates may be another long- term problematic issue in Hong Kong.

In future, new issues such a s the impact of new and more restrictive euidelines of waste disoosal should he cov- ered. The additional water charges (i0%) imposed upon factories for waste treatment to be enforced next vear. Bv then the relocation of factory in China to bring down oi- eration cost and to escape from the restrictive environ- mental ordinance in Hong Kong will become a real busi- ness and ethical issue.

The large number of variables in our cases suggests that, in the end we may reach a no best solution outcome. From the real case materials (provided by the Hong Kong Productivity Council) we must not only focus on a few par- ticular issues hut also evaluate critically the priority of a wide range of factors, as managers always do. As a n illus- tration, students were asked to assess the economic im-

Table 2. Enumeration of the Estimated Capital Costs (US dollars) for the Recommended Treatment System for Small, Medium, and

Large Size Electroplating Factories a

Factory Size Equipment Description Small Medium Large

Waste water transfer unit (pump etc.) 330 670 1170

Treatment unit (reaction tank, stirrer, filter, etc.) 2720~

Cyanide oxidation unit (oxidation tank, pH, and Redox 3600 4580 potential controller) Chromium reduction unit (reduction tank, pH and Redox 3300 4000 potential controller)

Precipitation unit (Flocculation tank and stirrer precipita- 5200 8700 lion tank, sedimentation tank, pH controller)

Sludge dewatering unit 1040 1603 Chemical dosing unit (acid dosing, caustic dosing, etc.) 1970

Automatic control unit (pH controller and Redox poten- 2170 tial controller) Installation (electrical wiring, plumbing) 1500

Operating cost (per month) chemical electricity labor Ooeratino cost oer volume of discharae (oer m3\ 1.7 0.6 0.4 ~, " . - ,,

' Information from the Division of Environmental Management, Hong Kong Productivity Council 1990. The inflation rate in Hong Kong runs at about 9% pa. ovbr the past three years and the cost to date might have increased by 20%. Equipment are designed and manufactured locally.

aAn integrated system.

526 Journal of Chemical Education

pact of the Ni recovery system in small factories. The cost of the equipment will be largely additional to that already recommended. A comparison with the amount of nickel re- covered will give a good indicator. Interactive handouts which contain notes, questions, and space for students to make comments also are designed to help students to fol- low in-lecture activity. Hopefully such materials will be published shortly.

Precaution and Assessment Care is particularly essential for the effective implemen-

tation of a less than conventional teaching methodology to immature or passive students. Such students resist new learning formats and thev have difficulty in forming their own opinions. More preparation for the Elass and mire ef- fective communication with students throughout the course are required. Excessive student involvement in class without Drover suvewision from teachers, ex., sum- . . mer" of;irguments, cnn fivt! students the false imprtr~sion that the teacher does not discharge his autv responsibly Idcally speak~ng, the n:a~mmended answer is just a refcr- ence for .zrudvnts to develop their dc.cision-making ab~l i ty Htnwvrr. it still has the tendfmcy tu t~ecome the olfirial "best" answer.

Jus t like assessment of project work, assessment of case studs is more difficult than the usual allocation of numeri- cal mades to rizht or wrone answers that tends to distract - u u

the student's attention away from learning. I t would be de- sirable to vrovide onlv aualitative assessment initiallv in " . various skills of judgment and establishing consensus within a erouv in order to encourage students to improve - . themselves. I place emphasis on weighting of each type of skill we considered to be of significant in a particular case. Again students should he informed on the guidelines for such choice. Until I was confident that they reach a certain level of proficiency in their skill, a quantitative assessment is given.

Conclusion We run our revised program over a brief period of a few

months with a new group of student. Already I see the

emergence of enthusiasm among most of them through their active involvement. Remettablv, because of the lim- ited time and the large class, there is not much room for them to develop verbal presentation skills.

Perhaps they can now see the subject is open, more lively than the descriptions found in many textbooks. The pro- gram gives them a good idea about the knowledge, skill, and flexibility which a manager needs. The op~ortuuity in research a n d development aiso provide anoihir means of broadening their minds. Certainly the course materials are open f; further extension. or-example, the economic factors, such a s the operation cost, vary from country to country. Different criteria of evaluation of pollution treat- ment methods may be necessary The application of science to deal with real ~roblems is. indeed. intellectuallv chal- lenging.

The implementation of the case study method undoubt- edly requires a great deal of our time and effort. In the end I had to remove one of the tovics mescribed in the orieinal . . - course outline to make the time for case analysis. However, I believe that in the lone term the additional effort bv all of us would prove worthwhile.

Acknowledgment I would like to thank my former students and K. L.

'bang, former HKPC staff, for their contribution in my teaching program. Also thanks are due to Mary Keitel, ETU, Hong Kong Polytechnic, who sharpened up my knowledge of the idea about a case study The valuable suggestions from the referee are most gratefully appreci- ated.

Literature Cited

6. Churbuek. D. C.Forbcs 1992.June 8.130. 7. Casex R. J.: Frazer M. J.I'i_ohlmi Solvinpiri theChemi~niIndurfiy; Pitman: London.

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