The European Union stipulated in directive 91/271/EEC of 21st May 1991 that
high nitrogen removal is expected for wastewater effluent of coastal cities
with greater than 10,000 inhabitants. The nitrogen removal efficiency of the
Luleå municipality (kommun) Uddebo wastewater treatment plant (WWTP) that
process wastewater of 75,000 p.e was investigated. The wastewater effluent
from the Uddebo plant which employ the trickling filter (TF) that operate at
13% removal efficiency was evaluated and a nitrogen mass balance on the whole
wastewater processing was estimated yielding a nitrogen content of 874kg N/d
as against the 374kg N/d stipulated by the EU. The result showed that the
nitrogen content in the effluent is not satisfactory, it far exceeds the
discharge limit, and further treatment techniques or technologies were needed
to help Luleå municipality fulfil the effluent quality. Biological nitrogen
reduction by bacteria involving two processes in sequence namely
nitrification and denitrification forms the basis for high nitrogen removal
from wastewater. In theory, the nitrogen in the wastewater would be converted
to nitrogen gas. A wide range of treatment processes and alternatives were
discussed. After careful evaluation of all available treatment technologies
and options, three were identified as the best suited for Luleå municipality:
upgrading to a moving bed biofilm reactor (MBBR), using wetlands for some
part of the municipality wastewater, and using urine diversion system for
part of Luleå city wastewater. For a better effluent result, the options were
grouped into four alternatives which include: (1) Upgrading the Uddebo plant
to MBBR (2) Constructed wetlands for areas with 1,000 or fewer inhabitants
plus MBBR for remaining municipal wastewater (3) Urine diversion for part of
Luleå city plus MBBR for the remaining wastewater (4) Mixed wastewater
treatment system with wetlands, urine diversion and MBBR process.
A detailed evaluation of the alternatives was done based on efficiency,
reliability and recycling potentials. The overall result showed that the
moving bed biofilm reactor is the best choice for the Uddebo wastewater
treatment plant in order to attain the desired 15 mg/l nitrogen concentration
in the effluent at 70...
