Research Trends and Results
Maintenance of Good Water Environments by Wastewater
Treatment and Evaluation of Sustainable Wastewater Treatment
Methods
YAMASHITA Hiromasa, Head; TAJIMA Atsushi, Senior Researcher; SHIGEMURA Hiroyuki,Senior Researcher; OGOSHI Masashi (D.Eng.), Researcher; FUJII Tsuyako, Researcher;
HAMADA Tomoyuki, Researcher
Wastewater and Sludge Management Division, Water Quality Control Department
Keywords: coliform count, coliform group count, energy consumption, nitrogen removal, reclaimed wastewater

1. Introduction
Sewage systems greatly contribute to the maintenanceof a good water environment, and for that purpose, theremoval of harmful microorganisms, organic matter andnutrient salts in sewage is important. Moreover, efforts toreduce energy consumption related to wastewater
treatment are important for achieving a sustainableenvironment. This division is conducting research andstudies from various viewpoints into the maintenance of agood water environment by wastewater treatment.
2. Study on introducing new hygienic indexes
to wastewater treatment facilities"Coliform group count" has been used as anenvironmental standard for water quality and as ahygienic index for final effluent from wastewater
treatment facilities since it allows for easy andcost-saving measurement. However, its validity as anindex of fecal contamination is pointed out to be low
mainly because of contained bacteria of soil origin. At
present, surveys and studies on reference values areproceeding in order to change the index used in theenvironmental standard for water quality from a roughcoliform count to measurable E.coli count." Therefore,
the need is growing for studies into changing the index toE.coli count also for effluent

Photo: Appearance of Coliform Colonies(Blue: E.coli count, Red: Coliform group count(except E.coli))
The NILIM is conducting a survey to grasp the E.coli
count in effluent, variations thereof by season and time ofday, the effect on measurement values due to the difference
among multiple measurement methods, etc. The survey
has so far revealed variations in the measured E.coli countaccording to the measuring method used for final effluent.
Variations according to seasons or time of day were notclearly seen. These results are to be utilized to study themethods for measuring E.coli count.
3. Study on reduction of energy consumption
related to nitrogen removal
Since energy efficiency in nitrogen removal is low insmall-scale wastewater treatment facilities, we studied
whether energy consumption could be reduced in thewhole drainage basin by integrating the pollution load
removal and associated energy consumption of multiple
wastewater treatment facilities in the same basin into alarge-scale wastewater treatment facilities. Using theSewage Statistics in Japan (note), we organized therelationship between energy consumption (kL/day),obtained by converting into quantity of heavy oil fromelectric power used in wastewater treatment facilities forwater treatment, and the nitrogen removal load (tN/day).
And we developed formula showing the relationshipbetween the nitrogen removal load (tN/day) and theenergy consumption (kL/tN) per unit removal amount,since energy efficiency changes according to the scale ofthe facilities. With this formula, we calculated energy
consumption in five small and large treatment facilities in
the model drainage basin, and studied whether it ispossible to reduce energy consumption while ensuring
the amount of removal by concentrating nitrogen
treatment in a large facility. As the result, it wasestimated possible to reduce 16% of the energy
consumption required for water treatment in the whole
drainage basin.
4. Evaluation of energy consumption related toreclaimed wastewater supplyReclaimed wastewater from sewage is a valuable water
resource available even in times of drought. Since theutilization of reclaimed wastewater needs to consider
energy consumption, we are studying reclaimed
wastewater processes that minimize energy consumption.
So far, we have found that, when a large amount ofenergy is consumed to convey reclaimed wastewater,
there is room to reduce consumption by screening supply
areas. We are proceeding to evaluate energy consumption
and life cycle CO2 assessment related to reclaimed
wastewater supply.
[Reference]"2009 Sewage Statistics in Japan", Japan Sewage Works
Association, June 2011