Iwa international Specialist Conference

T. I. Onyeche*; S. Schaefer*

Abstract:
The high sewage sludge production in Europe is estimated at almost 9 million tons per year with the value estimated at 12 tons by year 2005. An average of 5.6 million tons of sewage sludge are used or disposed of each year in the United States, and 60 percent of that is used for land application. Generally, there is a serious lack of health-related information about populations exposed to treated sewage sludge. The major part of sewage sludge is incinerated, land filled or applied on farms as fertiliser. Even farmers in some parts of Europe are now reluctant to apply sludge on their farms due to the concentrations of contaminants such as organic substances and heavy metals. Costs of sludge disposal vary widely depending on the location, level and type of contaminations. There is very high demand on reduction of sewage sludge and its contained organic substances worldwide.
Some researchers have published papers on sewage sludge treatments and their effects on the subsequent anaerobic digestion. But little has been published on the energy balance after such applications. Few works show improved anaerobic digestion with increased biogas production but with negative energy balance and such works are restricted to the laboratory. Combination of sludge treatment processes demands high costs on investment, operation and maintenance.
This paper aims at presenting preliminary results from tests carried out at an existing wastewater treatment plant. Results show improved anaerobic digestion, enhanced biogas production and reduced sewage sludge production. The sludge’s cytoplasmic light organic substances were liberated by mechanical cell disruption process using a modified high pressure homogeniser at relatively lower pressures. Energy produced in form of biogas (methane) replenishes the energy consumed during the cell disruption and anaerobic digestion processes. Concentration of sludge before mechanical disruption enhances the biogas (energy) production and sludge reduction. Results from wastewater treatment plant showed that about 25 % extra energy could be produced with about 24 % sewage sludge reduction, which further confirm the preliminary laboratory results already published.
Therefore, this paper presents the first tested and confirmed positive results at technical scale with appreciable energy production and sludge reduction. The excess energy produced can be used for local electricity production or for heating the digestion tower while the sludge reduction provides financial savings on disposal costs, which amounts to millions of US Dollars annually depending on the type of sewage sludge, the standard and capacity of the treatment plant in question.

Contact: Dr. Theodore I. Onyeche

CUTEC-Institut GmbH

Leibnizstr. 21+23,

D-38678 Clausthal Zellerfeld, Germany. [e-mail]

67.

Recycling of Phosphorus from Wastewater

Peter Balmér, Ola Palm and Erik Kärrman

Abstract

Phosphorus is an element essential for all biological life. The phosphorus resources of the world are limited. This was the reason why a committee, appointed by the Swedish government, a few years ago proposed that a 75 % recirculation of phosphorus from wastewater should be attained before 2015as one step towards a sustainable development of society.

The Swedish Environmental Protection Agency was recently requested by the Government to make a plan for the recirculation of phosphorus from wastewater. The EPA asked a group of researchers to investigate the possibilities.
The group looked into the recirculation of phosphorus by the use of wastewater sludge, by the use of source separated urine, by the use of source separated toilet water, by the use of phosphorus recovered from wastewater, by the use of phosphorus recovered from sludge and by the use of phosphorus recovered from the ashes from the incineration of sludge.
As the municipalities have to get rid of the sludge all alternatives were compared to a reference alternative that was incineration of sludge. The alternatives were evaluated with the criteria: possible recovery of phosphorus, possible recovery of other nutrients, environmental effects, resource consumption, organisational requirements, user’s attitudes and behaviours and economy.
2002-10-20

PS the study was performed by a group of 14 researchers. This means that the paper may get more authors.

68.

Recovery of phosphate from sewage – a Dutch analysis

Paul Roeleveld ,

Grontmij Water and Waste, The Netherlands

[e-mail]

Introduction

In the industrialised world, the interest in phosphate recycling is steadily increasing. On the Second International Conference on the recovery of phosphorus from sewage and animal wastes (Noordwijkerhout, The Netherlands, March 2001), it was concluded that phosphate recycling is now desirable and technically feasible, as shown by the handful of plants already operational across the world. There is a considerable practical interest in P-recovery from water companies, phosphorus industry and regulators, in a number of countries. The practical development of P-recovery, however, clearly depends strongly on local factors such as sewage works configuration, sludge management options, local markets for recovered phosphates and regulatory pressures. (A small summary of the Second Conference will be given in the full paper).

A Dutch analysis

In order to reduce the consumption of phosphate rock and to close the phosphorus cycle, the phosphorus industry Thermphos International B.V. from The Netherlands, has stated the objective of replacing 20% of its current phosphate rock consumption by recovered phosphates. Because municipal wastewater is a potential source of recovered phosphates, a study was carried out which focused on the quality and quantity of available phosphates in recovered materials from sewage treatment plants and sewage sludge processors. Based on defined quality criteria, the current and future technical feasibility of using these recovered phosphates as a raw material for the phosphorus production process of Thermphos International B.V. was assessed. Three streams were identified as potential sources for recovered phosphate:

1. 
   sewage sludge (chem-P and bio-P);
   
2. 
   end-products of sewage sludge processing (incineration, drying, composting);
   
3. 
   and phosphate products from side-stream processes (bio-P).