A `settler` models a secondary clarifier — the sludge-separation stage that sits downstream of a biological reactor. It receives the upstream reactor's effluent stream, performs a 13-species TSS mass balance, and splits the result into three Fluent envelopes: clarified effluent, surplus sludge, and return sludge. A downstream return pump (a `rotatingMachine` registered as `machine` / `downstream`) draws the return-sludge flow.
> Pending full node review (2026-05). Content reflects `CONTRACT.md` and current source only. The shipped `examples/` folder ships stubs only — production-grade flows are still TODO. Treat this page as informative, not authoritative.
| What it represents | Secondary clarifier / sludge settler — the gravity-separation stage between a biological reactor and its downstream sludge handling |
| S88 level | Unit |
| Use it when | You have a reactor whose effluent must be split into clarified water + return / surplus sludge by a TSS mass balance |
| Don't use it for | Primary sedimentation (species 7–12 zeroing is wrong), generic mass-balance transforms (the 13-species ASM3 vector is hard-coded), single-tank SBRs that don't need a 3-stream split |
| Children it accepts | `measurement` (any, but `quantity (tss)` is the only one that mutates state), `reactor` (upstream), `machine` (downstream — the return pump) |
| Parents it talks to | Typically a downstream `reactor` — the three Fluent streams are routed by `payload.inlet` |
S88 colours are anchored in `.claude/rules/node-red-flow-layout.md`. The settler editor colour is currently `#e4a363` (orange) — tracked as drift in §16 of that rule; diagrams in this wiki use the correct Unit blue (`#50a8d9`).
> The shipped examples (`examples/basic.flow.json`, `integration.flow.json`, `edge.flow.json`) are skeleton stubs — they create a settler node and a debug tap, but do not exercise the reactor → settler → pump chain. A proper Tier-1 / Tier-2 / Tier-3 example set is on the TODO list; until then this section walks the minimum stimulus.
| `data.influent` | `influent`, `setInfluent` | `{F: number, C: number[13]}` — either field optional | Override the influent stream directly. Triggers a recompute of all three Fluent envelopes. |
| `child.register` | `registerChild` | `string` (child node id) | Register a `measurement`, `reactor`, or `machine` child. Port 2 wiring does this automatically in normal flows. |
That is the entire input contract. Settler has no FSM, no setpoint, no startup sequence — it is a stateless transform on top of whatever the upstream reactor + measurement children push into it.
Port 1 (InfluxDB) is the scalar dashboard view — see [Reference — Contracts](Reference-Contracts#data-model--getoutput-shape). Port 2 carries the one-shot `child.register` upward at startup.
