The influence of bleaching techniques on properties of sulphate pulps of their bleach- effluents

anglais. Most of the chemical pulp industries in Indonesia are using the kraft or sulphate process. One of the weaknesses in this process is producing pulp with low brightness degree, thereby requiring a more effective bleaching technique. Elemental chlorine-bleaching agents can do this task effectively, unfortunately, their effluents are hazardous to the environments. Since then there have been developed some improved techniques by implementing, among others an elemental chlorine free (ECF) bleaching process. This is intended to eliminate or reduce the hazardous bleach-effluent impacts. This bleaching investigation used wood species of ampupu (Eucalyptus urophylla) and sampinur bunga (Podocarpus sp.) from North Sumatra. At first, those two species were each pulped using sulphate process with 17 percent alkali active, 25 percent sulphidity, maximum temperature at 170 degree Celcius, 4 hours cooking duration, and 1:4 wood to cooking liquor ratio. The introduced bleaching processes were C/DEoDED, DEopDED, DEoDEpD and CEHEH as a control. Results showed that the use of CEHEH technique and its modification into C/DEoDED, DEopDED and DEoDEpD technique for bleaching of ampupu sulphate pulp turned out to have their bleached pulp yields comparable to each other. In sampinur bunga sulphate pulp, on the other hand, different bleaching technique produced pulps with yields significantly different from one to the other. However, the overall bleached pulp yield of sampinur bunga were below those of chemical pulp in common (less than 40 percent). The bleached pulp yield of ampupu were greater than those of sampinur bunga (above 40 percent). Generally speaking, most of the bleached pulp strengths of sampinur bunga were higher than those of ampupu. In a more specific case, modification of CEHEH technique with no or reduced amount of elemental chlorine resulted in the bleached pulp strengths which were not significantly different. The BOD and COD values in the effluents from the overall bleaching techniques of ampupu were lower, and therefore considered better than those of sampinur bunga. Modification of the conventional bleaching technique (CEHEH) without the use of elemental chlorine (i.e. DEopDED and DEoDEpD) in either ampupu or sampinur bunga pulps could improve the alkalinity (increasing the pH) and reduce the residual chlorine content in their bleach effluents, but unfortunately was still unable to lower the BOD and COD to the satisfactory or safe levels

indonésien. Di Indonesia pengolahan pulp kimia berbahan baku kayu umumnya menggunakan proses sulfat. Salah satu kelemahan proses sulfat ialah derajat kecerahan pulp yang rendah, sehingga memerlukan teknik pemutihan yang efektif. Saat ini mulai dikembangkan teknik pemutihan pulp dengan pengurangan dan atau tanpa penggunaan klorin elementer untuk menekan pencemaran lingkungan. Penelitian ini menggunakan kayu ampupu (Eucalypitus urophylla) dan sampinur bunga (Podocarpus sp.) asal dari Sumatera Utara. Pembuatan pulp ini menggunakan proses sulfat dengan kondisi pemasakan: alkali aktif 17 persen, sulfiditas 25 persen, suhu maksimum 170 derajat Celcius, waktu pemasakan 4 jam dan bobot kayu banding larutan pemasak 1:4. teknik pemutihan yang diterapkan adalah C/DEoDED, DEopDED, DEoDEpD dan CEHEH sebagai pembanding. Hasil penelitian menunjukkan bahwa pada pulp kayu ampupu, modifikasi teknik pemutihan dari CEHEH menjadi C/DEoDED, DEopDED dan DEoDEpD menghasilkan rendemen pulp putih yang tidak berbeda. Pada pulp kayu sampinur bunga perbedaan teknik pemutihan menghasilkan rendemen pulp putih yang berbeda tetapi semuanya di bawah rendemen yang umum diperoleh dengan proses kimia (kurang dari 40 persen). Rendemen pulp putih kayu ampupu lebih tinggi dibandingkan pulp asal kayu sampinur bunga. Secara umum dapat dikatakan bahwa keteguhan pulp sampinur bunga lebih tinggi daripada kayu ampupu. Modifikasi teknik pemutihan CEHEH menjadi teknik pemutihan menggunakan pengurangan atau tanpa menggunakan klorin elementer menghasilkan kekuatan lembaran pulp yang tidak berbeda. Nilai BOD dan COD limbah cair pemutihan asal kayu ampupu lebih rendah dan lebih baik dibandingkan asal kayu sampinur bunga. Modifikasi teknik pemutihan konvensional (CEHEH) dengan teknik pemutihan tanpa menggunakan klorin elementer yaitu DEopDED dan DEoDEpD dapat memperbaiki pH dan sisa klor dalam limbah cair pemutihan pulp baik pada kayu ampupu maupun sampinur bunga, namun belum memperbaiki nilai BOD dan COD