Page 107 - Energy from Toxic Organic Waste for Heat and Power Generation

92 Energy from Toxic Organic Waste for Heat and Power Generation

for reuse in the paper making process [23]. Microwave pyrolysis, believed
as an enhanced rapid pyrolysis method, has also been tested on paper and
board industry sludge [29].

7.4.4 Anaerobic Digestion
Anaerobic digestion (AD) is a sequence of processes that involve microor-
ganisms breakdown of organic matter in the absence of oxygen. As a waste-
water treatment opportunity, AD is more well-known process in paper and
board industries, particularly in PfR utilizing mills owing to high-chemical
oxygen demand (COD) levels of its wastewater, existence of well- digestible
starch, and stumpy intensity of toxic/inhibitory compounds. AD can af-
fect 58%–90% chemical oxygen demand removal under such circumstances
3
in addition to production of 0.24–0.4 m CH 4 /kg COD removed [30].
Utilization of AD for transferring 25% of the globally available COD in
the wastewater of the pulp and paper industry into biogas can affect upto
1–100 TWh electricity generation annually [30]. Compilation of anaero-
bic wastewater treatment with aerobic posttreatment should be done for
increasing the quality of final water coming out to the surface. This compi-
lation will generate small quantity of wastes and only demands lower space
than standalone aerobic treatment.
As an option to handle bio-solids (WAS—waste activated sludge), anaer-
obic digestion is gaining interest currently from paper and board industry
aerobic wastewater treatment. The key block/interruption in this is com-
plex organic matter hydrolysis and many researches were done to overcome
this hindrance through mechanical, thermal, chemical, or biological pro-
cesses [30–36]. Around 30%–70% of solid wastes can be reduced via anaer-
obic digestion of waste activated sludge [31], in addition to the production
of CH 4 . It can also increase the waste activated sludge dewatering which
will reduce the utilization of dewatering chemicals [37].
Redirecting the waste activated sludge to AD can enhance the efficiency
of mechanical dewatering, as well as efficiency of incineration in industries
particularly where primary and secondary sludge are blended for dewater-
ing [38]. The reject water produced from this AD technique is nutrient-rich
that could be recirculated to the aerobic treatment, thus reducing the re-
quirement for nutrients addition. Further, the digestate can be processed to
commercial fertilizers.

7.4.5 Biodiesel
The integrated toxic contents subtraction and sustainable biodiesel inven-
tion also can be utilized for the pulp and paper industry effluents [39–41].