The anaerobic treatment of wastewater has contributed to the field of environmental protection. Complex Experiments were studied to study the percentage reduction of NOx levels in conventional engine with jatropha oil with varied injection pressure at recommended injection timing and compared with conventional diesel engine. The NOx levels were studies at various values of BMEP. The effect of other parameters like void ratio, catalyst temperature, space velocity on nitrogen oxides in the exhaust was also studied. The NOx emission levels were controlled by means of selective catalytic reduction technique using the lanthanum ion exchanged zeolite, called catalyst-A and urea infused ion exchanged zeolite, called catalyst-B with different values of injector pressures in conventional engine with crude jatropha oil at peak load operations. The NOx levels were found to be decreased 25-30% using selective at analytic technique.