**6. Effluent treatment**

**Effluent Caustic** 

232 Global Wheat Production

**dosage (%)**

**Color times**

**Table 11.** Characteristics of effluent from wheat straw CTMP pulping [28].

**pH number**

**Figure 5.** Wheat straw CTMP pulp yield decreases with increment of caustic soda dosage [24, 28].

**Figure 6.** Pollutant load of effluent decreases with increment of pulp yield [24, 28].

**Pollutant load (kg/t)**

CTMP-1 3.0 5166 9.1 150 47.6 188.3 271 181 6.04 1.90 CTMP-2 4.0 5244 9.6 173 78.5 277.1 369 200 6.75 1.92 CTMP-3 5.0 6127 10.1 219 124.3 315.9 446 228 8.08 1.93

**TOC SS TS COD BOD5 TN TP**

It is clear that pollution load from pulping process can be decreased by increasing pulp yield. Liu and Fang [24] summarized a relationship between COD load (y) and pulp yield (x) of wheat straw pulping, i.e., y = 4929.58426–104.0789x + 0.5883x<sup>2</sup> , r<sup>2</sup> = 0.910. It was proven that effluent from wheat straw chemi-mechanical pulping has a good biodegradability contrasting with that from OCC (old corrugated container) pulping. Effluent from wheat straw CTMP pulping has been characterized and illustrated in **Table 12** [24].

The proposed flow diagram for installation of effluent treatment plant is illustrated in **Figure 7** [24].

Since less amount of chemicals is applied for wheat straw impregnation, the contaminant of such pulping effluent consists of low polymerized or monomolecular carbohydrate compounds, which are biodegradable. With consideration of effluent characteristics from each stage and quality requirements of process water, it is possible to reuse the used water in a short circuit after suitable individual specific treatment. If chemi-mechanical pulping line is going to be installed in recycled fiber pulping and papermaking mill, the integrated effluent from wheat straw CTMP or CMP line will contribute to improve biodegradability for recycled fiber pulping effluent, carefully considering the water balance, and it is possible to produce wheat straw chemi-mechanical pulps without consumption of any fresh water [17]. Therefore, the total volume of discharge effluent will not be increased. It means that the original effluent treatment can be operated with improvement of efficiency [17, 25, 27].


**Table 12.** Effluent characteristics from wheat straw CTMP pulping [24].

can prevent degradation of cellulose and provide wheat straw chemical pulps with good physic strength and drainability; and (3) high-efficient extraction washer for black liquor is helpful to increase the initial concentration of black liquor, resulting steam savings during thickening black liquor and also decrement of fresh water consumption in pulp washing stage [4, 8].

For instance, Quanlin Paper Group has successfully operated its chemical recovery system for wheat straw chemical pulping black liquor, with an alkali recovery rate of more than 85%, and its mid-stage water can be treated economically to meet an extremely strict effluent discharge standard (COD concentration is less than 60 mg/L). There are many new techniques applied in its wheat straw pulping line, such as application of flying hammer chipper to separate more non-fiber components and to improve uniform cooking effects resulting in short cooking time and lower chemical dosage, decrement of black liquor viscosity from 1000cp to less than 500cp (solid content (55%) and temperature (100°C)); a vertical replacement cooking digester with large ration of chips to water was installed, leading to significant chemical dosage decrement and initial concentration of black liquor increment to save evaporation cost and to obtain more

Although being a highly abundant aromatic feedstock, lignin is still largely regarded simply as a source for heat and power for the biorefining or pulping process that liberates the lignin. The lack of established processes that add value to the lignin component can be largely attributed to its chemical recalcitrance and structural complexity. Adding to this complexity, the lignin structure is highly dependent on both the feedstock and lignin isolation process [30]. However, a part of lignin could be converted into value-added products including bio-based aromatic chemicals, as well as building blocks for materials [31]. The soda lignin has more value than kraft lignin from wheat straw in manufacturing lignin-derivative compounds in terms of the industrial lignin structure and the lignin recovery cost [30, 32]. Lignosulfonates and their modified products have always been traditionally and extensively employed as a class of thinning agent for drilling fluids. SFP lignin is a kind of lignosulfonate in the waste

SO3

results showed that SFP lignin exerts three effects on drilling fluid dilution, foaming, and flocculation. Therefore, SFP lignin and its modified products can be used as a thinning and foaming agent for drilling fluids, as well as a flocculating agent for treating waste drilling

Wheat is a kind of annual vascular-bundled herbal arthrophyte with only internodes of about 68%w/w of the whole stalk being acceptable for pulping and the remainder of 20–30%, i.e., leaves-sheaths, leaves-blade, nodes, grain, debris, etc., being removed for chemical saving and pulp quality improvement as well as silica content decrements of black liquor from cooking at a commercial pulping process line. There are a series of pulping processes, such as

, HCHO, and AQ [33, 34]. Experimental

Wheat Straw Pulping for Paper and Paperboard Production

http://dx.doi.org/10.5772/intechopen.77274

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thickened black liquor which is a benefit for chemical recovery boiler [3, 4].

**7.2. Application of straw industrial lignin**

liquor from the pulping of wheat straw with Na<sup>2</sup>

fluids [34, 35].

**8. Conclusion**

**Figure 7.** Diagram of an effluent treatment plan [24].
