Tuvalet kağıtlarının fiziksel özellikleri ile atıksu sistemlerinde parçalanma davranışları arasındaki ilişkilerin araştırılması = Investigation of potential relations between physical characteristics of toilet papers and their disintegration behavior in wastewater systems

Abstract

Personal hygiene products such as toilet papers (TPs) are disposed of into solid waste bins or into sewer systems via toilets. In sewers, their transport and disintegration rely on factors such as pipe diameter and slope, wastewater flow rate and flow velocity, product characteristics such as physical strength, and frequency and amount of product discharge. In parallel, personal hygiene products can absorb wastewater constituents such as grease and/or they blend with inorganic wastes such as sand and clay. This mixture of waste materials accumulates over time and cause sewer backups in parts of sewer system (e.g., manholes), where flow velocity drops suddenly. As a result, household residents face property damages, financial costs and health risks due to sewer backups. Likewise, wastewater authorities spend considerable amount of time, energy, and public funds to rectify pipe blockages, and to repair or replace any equipment (e.g., pumps and grinders) that is clogged by flushed materials. Recent studies and field observations confirm that some toilet paper can be problematic for wastewater systems. A recent study reported that nonwoven products (e.g. papers and wipes) constituted 78% of all solids in municipal wastewater samples that they took periodically over a year at 12 critical points in Berlin, Germany. This study pointed out that nonwoven products such as wipes play a pivotal role in sewer overflows. Another study proposed that disintegration of flushable products rely on product characteristics such as physical strength, and turbulence level of wastewater flow. Guided by this theoretical approach, mathematical models were developed and laboratory experiments were conducted to verify theoretical foundations and to elucidate disintegration patterns of various flushable products (e.g., toilet papers) in representative sewer flow conditions. However, a critical gap in the literature is the lack of fundamental studies that can help define and distinguish flushable and non-flushable items. Specifically, physical and mechanical aspects, as well as, material compositions of flushable products such as toilet paper must be defined urgently to minimize sewer problems such as pump clogs. Within this framework, this study assesses potential relations between physical properties of TPs and their disintegration behavior in sewer systems. TPs are consumed more commonly, more frequently, and in more amounts than any other FP. As primary flushable products, TPs usually move and disintegrate along with wastewater flow, and usually do not cause any major problem in sewer networks. Therefore, their fundamental properties can set a basis to evaluate new FPs such as flushable wipes. In this context, various toilet paper samples were obtained from domestic and international sources. Then, each sample's physical properties including sheet mass, sheet thickness, sheet volume, grammage, specific volume and embossing were quantified and/or graded. Briefly, we measured length and width of a sheet, and computed its surface area (length x width). Then, we used a light microscope to measure sheet thickness, and multiplied the thickness with surface area to estimate sheet volume. We measured sheet mass gravimetrically. Then, we computed basis weight as sheet mass divided by surface area. We estimated specific volume as sheet volume divided by sheet mass. We measured physical chacteristics of TP samples in their regular and in-package states, as well as in their dry states, which were obtained by drying samples at 104 C for 24 h. Next, representative samples were selected for experimental evaluation of their physical breakdown in sewer systems. This assessment was carried out according to test protocols developed by the International Water Services Flushability Group (IWSFG). The IWSFG's protocol involves a test equipment called Slosh-box that is a framed-box (width = 30 cm, length = 45 cm, and depth = 30 cm) that rocks from one side to the other via mechanical means. For testing, a toilet paper sheet and 4 L of tap water are placed into Slosh-box and shaken together at an oscillation speed of 18 oscillations per minutes (opm) for 30 minutes. To pass, 80% of the initial dry mass of the sample must be <25 mm solids after 30 minutes of shaking. In view of the results, disintegration rates of toilet papers did not indicate any meaningful relationship along with sheet mass of the samples. A linear relationship was observed between sheet thicknesses and specific volumes of toilet papers and their disintegration rates. Toilet papers with thickness values <165 µm and specific volumes <3.5 dm3/kg disintegrated relatively rapidly, whereas TPs with thickness values >175 µm and with specific volumes >3.5 dm3/kg disintegrated relatively slowly. A noticable relationship was clear between sheet volumes of toilet papers and their disintegration rates. Simply, TPs with sheet volumes <2100 mm3 disintegrated rapdly, while products with sheet volumes above 2100 mm3 disintegrated relatively slowly. No meaningful relationship was detected between grammage of TPs and their disintegration rates. However, a linear relationship was detected between embossing of toilet papers and their physical breakup. In parallel, toilet paper's pulp components, such as fiber type, fiber dimension and chemical additives, influence disintegration rates of toilet papers. Hence, potential effects of pulp components on disintegration behavior of toilet papers must be evaluated along with physical properties of such products. When compared with past studies, our findings are new and original in relevance of connecting physical properties with disintegration behavior of TPs. Past studies mostly focused on issues within a certain field of study such as identification of product characteristics and/or improvement of products according to consumer expectations. However, the results from this study are interdisciplinary and aim to connect two important areas as how product properties relate to flushable characteristics. In this regard, our results are obtained by using 8 representative samples; thus, the findings must be verified by using larger number of samples. For instance, grammage values of the samples ranged from 34 to 57 g/m2, whereas one study reported this range as 16-38 g/m2 for products from North America. This comparison shows the need to verify our findings with numerous samples that indicate wide ranges for product properties. For potential impacts on wastewater systems, the findings indicate that toilet papers that are characteristically thick and dense are unsuitable for disposal into sewer systems. Their transport and disintegration in sewer pipes will be hindered as they blend with other wastes such fat, oil, and grease (FOG) that flow with wastewater. Continuous discharge of toilet papers into sewer systems will cause accumulations of solids in drainlines, small sewer pipes, bends, and manholes, while they will blend with other wastes such as wet wipes. Consequently, these mixtures of solid wastes will cause sewer backups, property damages, financial costs, and public health concerns. Hence, toilet papers as well as other flushable products must be defined and regulated urgently to ensure long-term sustainability of wastewater collection and treatment systems. Keywords: Toilet paper, wastewater system, physical characteristics, disintegration