High efficiency of drinking water treatment residual-based sintered ceramsite in biofilter for domestic wastewater treatment

Aluminum (Al)-based drinking water treatment residue (DWTR) has often been attempted to be recycled as dominant ingredient to produce sintered ceramsite for water treatment. This study aimed to determine the long-term performance of DWTR-based ceramsite in treating domestic wastewater based on a 385-d biofilter test and by using physicochemical, metagenomic, and metatranscriptomic analyses. The results showed that the ceramsite-packed biofilter exhibited high and stable capability in removing phosphorus (P) and chemical oxygen demand (COD), with removal efficiencies of 92.6 ± 3.97% and 81.1 ± 14.0% for total P and COD, respectively; moreover, 88-100% of ammonium-nitrogen (N) was normally converted, and the total N removal efficiency reached 80-86% under proper aeration. Further analysis suggested that the forms of the removed P in the ceramsite were mainly NH4F- and NaOH-extractable. Microbial communities in the ceramsite biofilter exhibited relatively high activity. Typically, various organic matter degradation-related genes (e.g., hemicellulose and starch degradations) were enriched, and a complete N-cycling pathway was established, which is beneficial for enriching microbes involved in ammonium-N conversion, especially Candidatus Brocadia, Candidatus Jettenia, Nitrosomonas, and Nitrospira. In addition, the structures of the ceramsite had high stability (e.g., compressive strength and major compositions). The ceramsites showed limited metal and metalloid pollution risks and even accumulated copper from the wastewater. These results demonstrate the high feasibility of applying ceramsite prepared from Al-based DWTR for water treatment.

Drinking water treatment residue recycled to synchronously control the pollution of polycyclic aromatic hydrocarbons and phosphorus in sediment from aquatic ecosystems

Great efforts have long been made to control sediment pollution from persistent organic pollutants and phosphorus for aquatic ecosystem restoration. This study proposed a novel recycling of drinking water treatment residue (DWTR) to synchronously control sediment polycyclic aromatic hydrocarbons (PAHs) and phosphorus pollution based on a 350-day incubation test. The results suggested that DWTR addition reduced approximately 88%- 96% of potential bioavailable PAHs and 76% of mobile phosphorus in sediment. The dominant mechanisms for both reductions by DWTR were immobilization, mainly through increasing sediment amorphous aluminum and iron. The tendency of enhanced PAHs degradation by DWTR was also observed, especially for high molecular weight PAHs (e.g., chrysene, indeno(1, 2, 3-cd)pyrene, and benzo(g, hi)perylene), which decreased by approximately 21.1%- 22.0% of the total. Additionally, accompanying a clear increase in the connections of microbial cooccurrence networks, the variations in bioavailable PAHs, amorphous aluminum and iron, and other properties (e.g., pH, nitrogen, and organic matter) significantly (p < 0.01) enhanced Flavobacterium enrichment, although the enrichment of many other microbes potentially related to PAHs degradation (e.g., C1-B045) decreased after DWTR addition. Therefore, DWTR could promote the construction of a "PAHs immobilization with microbial augmentation" system while immobilizing phosphorus in sediment, indicating the high feasibility of controlling multiple sediment pollution.