Tanzania: Hot Disposal in a Rotary Kiln
Tanzania: The waste introduction
system satisfies highest safety standards.
It took five years, until mid-1996, to dispose of all 57,600
liters of DNOC. As usual, the Pesticide Disposal Project had to do the
pioneering work: This was the first time that obsolete pesticides were to be
incinerated in a cement factorys rotary kiln directly in a developing
The history of this disposal project goes back to 1991, when the
International Red Locust Control Organisation for Central and Southern Africa
(IRLCO-CSA) recognized a need for action and turned to GTZ for help. Four
decades earlier, IRLCO-CSA had stockpiled large amounts of insecticides in the
traditional breeding grounds of the red locust in Tanzania and Zambia in order
to be ready just in case. The stocks included huge amounts of DNOC.
Due mainly to its persistence, 4,6 dinitro-o-cresol is a highly
toxic pollutant. This DNOC was stored too long under poor storage conditions.
Eventually, the corroded drums began to leak. The situation became more and more
dangerous, particularly at the Muse storage facility, where more than 50,000
liters of DNOC were stored, mostly in leaky drums and large steel tanks situated
just a few meters away from the banks of Rukwe Lake. The poison seeped into the
soil and, as the groundwater table rose during the rainy season, into the lake
as well. The resultant fish kill threatened the local populations natural
The Pesticide Disposal Project conducted a survey in 1992. The
possibility of local disposal was investigated, and the subsequent plan of
action regulated the safeguarding of the stocks and their transfer to
Dares-Salaam. It also envisaged the design of a facility in which the DNOC could
be incinerated in a cement kiln in line with stringent safety standards. This
waste introduction system (WIS) was designed as a mobile unit.
The Waste Introduction System was developed especially for the
disposal of liquid chemicals. It is a mobile unit that satisfies highest safety
Since the system operates under high pressure, it is equipped
with underpressure and overpressure safety devices and a splash guard for the
operators workstation. In addition, all essential components are
After the pesticides were incinerated, the original WIS was left
in place for future activities at the cement factory, since the like-method
disposal of additional chemical waste and veterinary products had since come
Safeguarding measures were commenced with in late 1993. Under
adverse logistical and climatic conditions, all 57,600 liters of DNOC stored at
the five different sites were filled into containers and transferred by rail to
Dar-es-Salaam, where an interim storage facility had been set up on the premises
of the Twiga Cement factory in Wazo Hill, where the DNOC was to be incinerated.
That took place in mid-1996 in the largest of the factorys
three rotary kilns. Bayer AG supported the measure by conducting the requisite
incineration trials in its own laboratories.
The 4,6 dinitro-o-cresol was diluted in kerosene to a
concentration of 20%. The resultant solution was pumped into the supply tank of
the WIS and diluted with diesel fuel to a residual concentration of roughly 10%.
A diaphragm pump injected the mixture under high pressure directly into the oil
lance of the cement kiln. The incineration temperature was situated above
1,850°C. Afterwards, the 450 empty drums were recycled, i.e., cleaned,
shredded and melted down at a local steelmaking plant.
In addition to the combustion gases, the process produced a
small amount of ash that was subsequently integrated into the hot clinker
(nearly 1,450°C) in the cement kiln. (Clinker is an aggregate used in the
production of cement.) During the entire program, the cement clinker and dust
were sampled but showed no indication of DNOC residue. The emissions were also
continuously monitored. No rise in NOx emissions was noted.
Tanzania: For the first time, a large
quantity of obsolete pesticides was incinerated directly in a cement kiln.
The actual incinerating process in particular led to some
substantial delays, most of which were attributable less to technical
difficulties than to administrative and social problems.
Clashes of competence between various authorities caused one
delay after another. In addition, the cement factory had not pursued an adequate
information policy, so at the beginning of the operation the employees were
distrustful of the planned activities. This was the first time that such a large
amount of obsolete pesticides was to be incinerated directly in a developing
country. There was defensiveness on the part of those who felt like guinea pigs.
It took an interdisciplinary team of representatives from various ministries and
the university to remedy the situation by backstopping the entire program and
monitoring the incineration process. Indeed, that team has since become
established as a fixture institution in Tanzania that is now
supposed to plan and backstop future hazardous waste disposal activities.
INCINERATION OF DNOC
4,6 dinitro-o-cresol is a very effective insecticide and
herbicide. It is also persistent and, in the dry state, explosive.
Its chemical structure is easier to break down than that of PCB
molecules, and there is no danger of polychlorinated diben-zodioxins or furanes
forming as a result.
Thus, the stack gas contains only CO, CO2,
H2O and NOx, all of which are expelled to the atmosphere. Waste DNOC
is regularly incinerated in Germany.