Iwa international Specialist Conference

75.

Utilization of Sludge in Building Materials

Nagaharu Okuno, Aya Shimizu

The University of Shiga Prefecture

[e-mail]

Several thermal solidification processes have been developed mainly in Japan. They are lightweight aggregates, marble (or granite) brick, interlocking tile, and slag. They are made from incinerated ash in general, but it is possible to make them from de-watered sludge cake, if you wish. (When starting from the de-watered cake, careful operation of the process is more important.) A full-scale plant of them has been successfully operated for more than 10 years. The quality of the end products is better than the traditional ones. They are all substitutive to existing ones.

The Japanese experience proves that all the processes are technically feasible, but not economically. Their manufacturing cost is always higher than market price. Non of them is competitive in market. However, if they are identified for a process of sludge disposal, all of them are worth considering for a big city where no place for the sludge to go. The end products can be recycled or reused inside the city.
A new alternative is ”Portland cement”. A Portland cement manufacturer accepts sewage sludge, if being paid some amount of money depending on moisture contents of sludge. If it is incinerated ash, an average payment is US$120 each 1000Kg of ash (or US$11.5 per 1000Kg of sludge cake). It is about 50 to 30 % of the energy cost of thermal solidification. The operation cost of this application is much cheaper than any thermal solidification process in house. Therefore, a sewage plant that has already an incinerator is more interested in a Portland cement application than the thermal solidification.
The next discussion is concentrated on ”what is the best pretreatment process for the Portland cement application” ---- de-watering, drying, carbonating, or incinerating. Another discussion is how much is the maximum allowable rate for the sludge to be blended with raw materials of the Portland cement. These are a main subject to be discussed at my session of this conference.

76.

Lightweight aggregates made from sludge
P.J.Wainwright & D.J.F. Cresswell

School Civil Engineering, University Leeds, England

ABSTRACT
The construction industry has the potential to provide a market for the use of many waste materials. However, to do so the products have to be of sufficient quality and consistency for the construction industry to accept them. The production of synthetic (artificial) aggregates is one potential high quality use of wastes.
Synthetic aggregate is currently produced from virgin materials (clay, shale, slate) and from pulverised fuel ash (PFA). The process involves processing the materials into the spherical shape desirable for aggregate utilisation, this process is termed pelletisation. The ‘pellets’ are then heated (usually in a rotary kiln or on a sinterstrand) until the individual particles fuse together producing the strength necessary for an aggregate, this is termed sintering. For the work presented in this paper the method of heating was by the use of an innovative design of rotary kiln.
Waste water sludge can act as a binder and as an alternative fuel source in the production of synthetic aggregates. The presence of organic matter and the inorganic material from the sludge during firing can alter the aggregate’s properties (density, water absorption, aggregate pore structure). This paper outlines a systematic investigation into the use of waste water sludge in synthetic aggregate production. Waste water sludge was added in varying amounts to two ‘inert’ wastes and the specimens were then fired under a variety of controlled conditions. Tests were conducted to assess the influence mix composition and firing conditions (e.g. temperature and time) on aggregates properties. The properties measured included porosity, water absorption, relative density and bulk density. From this information it will be possible to make a judgement as to the suitability of the synthetic aggregates for use as a replacement for natural aggregates in concrete. Tests to assess the influence of the aggregates on concrete properties will be carried out but the results will not be available for publication in the paper. The information obtained from the work presented in this paper and the future work on concrete properties will provide the first steps in helping in the design of a commercial process.
KEYWORDS: Synthetic aggregate; waste water sludge; rotary kiln; concrete

77.

FROM WASTEWATER SLUDGE TO PREDATOR PROTEIN

Klapwijk,Buys, Mulder, Rulkens

Wageningen UR
The paper is focused on the treatment of secondary wastewater treatment sludges by oligochaete aquatic worms. The aquatic oligochaetes are first used to accelerate the (aerobic) stabilisation of sludge and subsequently as a source of protein for the production of an industrial glue or coating. The process targeted thus consists of the following steps:

• Predation of sludge by aquatic oligochaetes

• Separation of the oligochaetes from the sludge

• Extraction and purification of protein from the oligochaetes

• Technical application of this protein.
Our results show that aerobic sludge stabilisation of secondary sludge grown on domestic wastewater, is enhanced by predation by aquatic oligochaetes: the stabilisation rate can increase up to a factor 2. The maximum degree of stabilisation is however unaffected by predation. Concomitantly with the progress of sludge stabilisation, the oligochaetes are shown to grow, as evidenced by an increase in oligochaete dry weight. The maximum growth yield is about 0.3-0.5 g/g of increase in worm-VSS per g of decrease in sludge-VSS.
Separation of larger oligochaetes from sludge may be performed by sieving (250 m). Different methods were tested to isolate and purify protein from Tubificids. Protein contents of different oligochaetes range from 50-70% of dry matter. Molecular weight (SDS-PAGE) and amino acid composition were determined. Amino acid composition was found to be comparable to that of haemoglobin. The formation of films with Tubificid protein was tested: the optimum temperature and pH and the effect of several additives on film formation were determined. The films were characterised and compared to films made with other widely applied proteins.
This research thus shows that secondary wastewater sludge can be converted into oligochaete protein, from which a good quality glue can be produced.

78.

Wastewater Sludge Management- Production of Value Added Products Through Bioconversion
S. Yan and R.D. Tyagi

I.N.R.S.-ETE, Université du Québec

Sainte-Foy, Québec, G1V 4C7 Canada

Phone : [phone], Fax : [phone]

E-mail : tyagi @inrs-ete.uquebec.ca
Abstract: The role of wastewater and wastewater sludge management continues to gain priority in terms of appropriate waste management/reuse. Recommended options of sludge management should lead to simple and safe management alternatives that stress reclamation of resources. This paper addresses the current sustainable strategies, priorities and future directions of waste management as it relates to the recovery of value added products using wastewater sludge as a raw material. Relatively new approaches, which are being developed, include bioconversion of sludge to different value added products: bioplastics, biofertilizers, biopesticides, enzymes etc. Sludge management and resource recovery approaches must be diversified and flexible. They should be based on actual needs of the affected society and community. It is also important that the chosen strategy be appropriate to the conditions of the site under consideration and process economics. Processes which promote sustainability will become viable options for resource management if conversion into ‘value added product’ can be realized. In many cases higher yield of products is achieved using sludge as a raw material than those obtained in conventional fermentation processes. The yield of Bacillus thuringiensis based biopesticides, for example, is twice that obtained in synthetic medium or industry standard. Similarly, the yield of other products (biofertilizers, alkaline proteases and bioplastics) is either comparable or higher than conventional processes. The most important factors that affect the product yield includes : sludge solids concentration, C :N ratio, availability of biodegradable carbon, sludge type and oxygen transfer. Detailed studies have been made to investigate these parameters. Wastewater sludge may pose many problems in biocoversion processes. This includes availability of biodegradable material, presence of pathogens, presence of contaminants, recovery of value added product and the end use of the product. Many methods have been developed or being developed to augment the availability of carbon and nitrogen in wastewater sludges to augment the yield of final product and productivity of the process. The problems and challenges in utilization of sludge as raw material for the production of value added products along with economic gains and sustainable management of sludge shall be addressed in this study.

79.

INTEGRATED, LONG TERM, SUSTAINABLE, COST EFFECTIVE BIOSOLIDS MANAGEMENT AT A LARGE CANADIAN WASTEWATER TREATMENT FACILITY
Ronald J. LeBlanc⁽¹⁾ Conrad J. Allain⁽¹⁾ Peter Laughton⁽²⁾ Glynn Henry^(3)
(1) Greater Moncton Sewerage Commission, 355 Hillsborough Road, Riverview, New Brunswick E1B 1S5, Canada

⁽²⁾ R.V. Anderson Associates Limited, Consulting Engineers, 2001 Sheppard Avenue East, Toronto, Ontario M2J 4Z8, Canada

⁽³⁾ Department of Civil Engineering, University of Toronto, 35 St. George Street, Galbraith Bldg., Toronto, Ontario M5S 1A4, Canada