Proceedings of the International Symposium on Efficient Water Use in Urban Areas


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Special Session: Special Speech & Introduction to IETC's "maESTro"

Changing the Concept of Sewage Works for Sustainable Society
-Separation of urine and feces for recovery of useful materials and stopping contamination of water bodies.

Saburo Matsui, Ph. D
Kyoto University, Graduate School of Engineering
Research Center for Environmental Quality Control
Yumihama, Otsu City, Japan

Introduction

Lakes and reservoirs are most vulnerable water bodies on the earth, where all contaminants converge on resulted in difficult harmonization among many users in terms of water quality. Among contaminants, the most common elements are nitrogen and phosphorus that are basic elements of food production. After the world war II, food shortage was serious any place of the world except US and a few countries. It was introduced so called Green Revolution in the agricultural sector, which was very successful to support necessary food supply for the most of population avoiding starvation. The factors involved in the success included the use of large amount of fertilizers, namely nitrogen and phosphorus, and application of synthetic agrochemicals, etc. Over use of fertilizers brought eutrophication problems in water bodies of lakes and reservoirs, and even closed seas. Eutrophication problem of freshwater becomes serious for drinking water supply as well as drinking water for cattle, sheep, etc. Even aquaculture faces difficulty with maintaining of the production of marketable species.

EU has introduced regulations on the use of fertilizers for control of eutrophication and ground water contamination from nitrate. Less number of countries have similar regulations. Over use of nitrogen brought another serious threat on the water environment, namely ground water contamination, which is also a problem for drinking water supply in many countries regardless developed and developing countries.

Nitrogen is a basic element in the global cycle between water and air that is the largest pool. After the world war II, nitrogen fixation from air into ammonia became large production. Comparing to the large amount of nitrogen fixation, it occurred less amount of denitrification, which upset the nitrogen cycle, resulted in the accumulation in nitrogen with surface water as well as ground water. Phosphorus is another important element for agriculture, but very effective for eutrophication of water bodies. Although it seems that the supply of this fertilizer is not limited so far, the mineral storage of phosphorus is not reassuring in the future, because that the origin of mineral phosphorus was the past birds feces.

It is necessary to find a solution of stopping water contamination due to over use of nitrogen and phosphorus. This paper tries to bring a new concept of sewage works that can provide a solution.

What are the differences between urine and feces in terms of nitrogen and phosphorus contents

It is very interesting to know the differences between urine and feces in terms of nitrogen and phosphorus contents. Table 1 shows that urine is rich with nitrogen (88%), phosphorus (67%), and potassium (71%), which may be different from the common sense of the people. Urine is free from pathogens that can be found only in feces.

Table 1 Nutrient distribution between urine and feces (After SEPA, 1995)


Parameter	Urine g/person/day	%	Feces g/person/day	%	Total discharge g/person/day	%

Wet weight	900-1200	90	70-140	10	1000-1400	100
Dry weight	60*	63	35	37	95	100
Nitrogen	11.0	88	1.5	12	12.5	100
Phosphorus	1.0	67	0.5	33	1.5	100
Potassium	2.5	71	1.0	29	3.5	100

*A large proportion of this dry substance is rapidly biodegradable. Much of it already degrades in the sewage pipes.

Table 2 provides the information of pollution loads of a person to the water environment. When it combines the data of Table 1 and 2, the following estimation can be drawn that urine contains 66% of nitrogen and 50.3% of phosphorus discharged by a person in the form of sewage.

Table 2 Pollution loads of waste water generated by a person (After Sewage Works Guideline, Ministry of Construction, Japan, 1996)


Item	Average g/person/day	Std. deviation	No. of Data	Urine + Feces %	Gray water %

BOD5	58	18	99	32	68
CODmn	26	9	96	36	64
SS	44	16	99	47	53
T-Nitrogen	11	3	9	75	25
T-Phosphorus	1.2	0.2	8	75	25

If we collect urine separated from feces, and treat in some way for the recovery of nutrients to provide to agricultural sector, we can reduce nitrogen and phosphorus loads on water bodies by replacing synthetic fertilizers. This is a practice of nutrients recycling from urban areas to agricultural areas, which is a key factor for building a sustainable society. This practice is also a promising solution for controlling eutrophication in lakes and reservoirs, and ground water contamination of nitrogen.

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